Caldara di Manziana (RM)

The Caldara di Manziana Natural Monument is reached from Via della Caldara, a side road of Provincial Road 2c that connects Manziana to Furbara station on Via Aurelia: about five kilometers from the center of Manziana you turn and continue for 500 meters of dirt road to a small parking lot, beyond which you walk on foot only. Entry is free and open, there is no ticket office, no turnstile, no posted opening hours: the area is open and for that reason the responsibility to behave well falls entirely on whoever arrives. By train you get off at Manziana-Canale Monterano station, on the regional railway that goes from Rome up toward Capranica and Viterbo, and from there you continue on foot through the woods for about seven kilometers. The site is classified as a Special Area of Conservation with the Natura 2000 code IT6030009, measures 90.42 hectares and the managing body is the Ente Parco Bracciano-Martignano, headquartered at Via Aurelio Saffi 4/a in Bracciano, telephone 06 99801176. Before leaving it's best to call or consult the Park's official website: the condition of the ground and the usability of the trails change with the season and the weather.

The Caldara is part of the Bracciano-Martignano Regional Natural Park, the protected area that holds together the two volcanic lakes and the wooded hills northwest of Rome.

A premise that is not rhetoric, and that should be read before getting in the car. At the Caldara di Manziana the ground emits gas continuously. Carbon dioxide is heavier than air and tends to stagnate in hollows, pits, low points, exactly where a child plays and where a dog sticks its nose. You do not go down into the central basin, you do not lie on the ground, you do not immerse yourself in the water, you do not let dogs run free. This is not an ordinary walk on a meadow: it is an active geothermal site, and it must be treated with the respect owed to a natural phenomenon that gives no discounts.

What the Caldara di Manziana really is

Whoever arrives for the first time expects a spectacular crater and instead finds a pale, almost lunar clearing, set into an amphitheater of trees. The Caldara di Manziana is a basin of volcanic origin of about 90 hectares, occupied at the center by a marsh of sulfurous waters where the water boils without being hot. This is the first misunderstanding to clear up: the bubbling is not boiling. The temperature of the mineralized spring is about 20 degrees Celsius, that is that of an April day. What moves the surface are the gas bubbles that rise from the subsoil and cross the layer of water.

The local name, the one still heard in the bars of Manziana, is callara: the cauldron, the pot. It is a name that perfectly describes what the eye sees and misunderstands what the thermometer measures.

The three environments of the Caldara di Manziana

Within a perimeter that can be walked in an hour of slow walking, three clearly distinct natural environments coexist, and this coexistence is the reason the site is considered one of the most important biotopes in central Italy:

• the marsh of sulfurous waters, at the center of the basin, with the bubbling springs,
• the birch grove, on the outer edge of the crater, on clay ground,
• the peat bog, which forms in the spots where water stagnates above impermeable muds.

Three environments that elsewhere are found hundreds of kilometers apart from each other. Here they touch. A botanist would read them as three chapters of different climates bound by mistake into the same volume.

The essential fact sheet of the Caldara di Manziana

Municipality of Manziana, province of Rome. Elevation around 250 meters above sea level. Area of the Special Area of Conservation: 90.42 hectares. Natura 2000 code: IT6030009. Conservation measures adopted with resolution of the Lazio Regional Council no. 159 of April 14, 2016. Managing body identified with resolution no. 305 of June 19, 2018. The area, originally protected as a natural monument, is today included in the Bracciano-Martignano Regional Natural Park, established by the Lazio Region with the regional law of November 25, 1999. On July 19, 2006 the European Commission, with decision 2006/613/EC, included the Caldara di Manziana in the list of sites of Community importance for the Mediterranean biogeographic region, with that code IT6030009 which today identifies it in all official documents.

Safety at the Caldara di Manziana: the gases are not a detail

Let's talk about the serious thing, and let's talk about it first, because the rest is filler. The floor of the Caldara di Manziana basin emits a continuous flow of gas, made up in very large part of carbon dioxide and, in smaller share, of hydrogen sulfide, methane and minor components. Hydrogen sulfide is the one you smell: the rotten-egg odor that accompanies the visitor from the parking lot on and that many find unpleasant from the very first steps.

Why carbon dioxide is the problem

Carbon dioxide has no smell and no color. It's denser than air, and so it doesn't disperse upward the way smoke would: it slides downward and accumulates in depressions, holes, basins, hollows, ditches. On a windy day the mixing of the air disperses it. On a still, humid day, without a breath of wind, the concentration at ground level can rise. Degassing sites must be visited with your head, not with the urge for a close-up photo.

The rules to respect at the Caldara di Manziana

They're few and they allow no exceptions. You don't go down into the swampy basin and you don't leave the beaten paths. You don't immerse yourself in the water and you don't drink it: the water is mineralized and crossed by gas, it isn't an equipped thermal pool. You don't lie on the ground and you don't sleep outdoors in the area. Children must be held by the hand and never left to run toward the pools: they're shorter than an adult, and so they breathe closer to the layer where the gas stagnates. Dogs must be kept on a leash, always, for the same reason multiplied: a dog walks with its nose 20 centimeters from the ground, that is exactly at the worst point. No fires, no barbecues, no lit cigarettes in an environment where methane also surfaces.

The safety advice on the Caldara di Manziana

If you arrive and find still air, low haze, sultry heat with no wind, look at the basin from the high edge and give up on getting close to the pools. You aren't missing anything essential: the Caldara is better understood from the rim of the crater than from the bottom. And if someone in the group reports a headache, dizziness, shortness of breath or nausea, you go back up immediately, toward the high ground and the open air, without discussion. This is the only page of this guide that I ask you to read twice.

The bubbling pool of the Caldara di Manziana

The central zone of the Caldara is occupied by a swamp in which the water bubbles in several pools, pushed by the gas emissions that rise from below. The main component of those emissions is carbon dioxide. The noise is thin, intermittent, a murmur you hear only if the group stops talking: whoever accompanies visitors to this place knows that the best moment of the visit is when silence is imposed for 30 seconds.

How the swamp formed

The swamp is the result of very slow work. On the floor of the basin, clay minerals have been deposited over time, forming a thick layer, of a color between white and yellow. That layer is impermeable: it holds the rainwater and the water arriving from the surrounding streams, keeping it from seeping into the depths. Without that clay cap there would be no standing water, and without standing water there would be neither swamp nor peat bog. The Caldara di Manziana exists as we see it thanks to a detail of sedimentology.

Secondary volcanism explained well

The phenomenon of bubbling pools is a textbook example of secondary volcanism: there is no lava, no active eruptive vent, no danger of eruption. There is the rise of gas flows toward the surface and their interaction with surface water. In the specific case of Manziana, these flows generally rise from depths of thousands of meters, over 2,000, and are made up 98-99 percent of carbon dioxide. The remainder is hydrogen sulfide, methane and minor components.

Where the carbon dioxide comes from

Carbon dioxide originates in the carbonate rocks present at those depths: subjected to high temperatures, above 200 degrees, they undergo decarbonation reactions that release gas. It's a process with nothing exceptional about it in the Earth's crust, but here it finds a concentrated and visible way out. Hydrogen sulfide has a similar origin, most probably associated with the reduction of sulfate rocks in the presence of carbon dioxide.

The smell of the Caldara di Manziana

When hydrogen sulfide reaches the surface it oxidizes, releasing hydrogen ions and sulfur oxides. They are responsible for the characteristic smell you notice at the Caldara di Manziana and in many thermal localities in the surroundings. It's a smell that stops bothering you after 10 minutes, and that stays stuck to your clothes until evening. Anyone planning an elegant dinner after the visit has been warned.

The color of the floor

The yellowish white of the muds, the milky water, the ocher halos where sulfur deposits: the palette of the Caldara di Manziana is that of an Icelandic landscape transplanted 50 kilometers from the Colosseum. It's the reason this place has appeared for decades in lists of absurd places near Rome, and for once the list is right.

The birch grove of the Caldara di Manziana

The vegetation of the Caldara is overall what you expect from Tyrrhenian central Italy: Mediterranean scrub and deciduous oak woods, with the Turkey oak ruling in the woods around. Then you reach the outer edge of the crater, on clay ground, and enter a grove of white birches, Betula pendula. Pale bark, thin trunks, small leaves that tremble at every breath of air. A piece of Scandinavia at 250 meters of elevation, an hour by car from the Grande Raccordo Anulare.

Why the birches here are an anomaly

The white birch is a species of northern territories and cold climates. In Italy it is commonly found in the Alps and the high-altitude Apennines, not in a Lazio basin a few dozen kilometers from the sea. Its presence at the Caldara di Manziana is a recognized botanical rarity, and it is one of the reasons the site obtained Community protection.

The two hypotheses on the origin of the birch grove

At least two explanations circulate about the origin of this grove, and they should be kept distinct by degree of certainty, because neither of the two is definitively proven. The first, the most fascinating, holds that the local conditions of the Caldara, with its swamp and constant humidity, created a microclimate favorable to the survival of the birch: the birch grove would then be a relic of a period after the glaciations, when cold-climate species descended much farther south and then retreated, leaving some populations isolated. The second hypothesis, more prosaic, is that the grove is of artificial origin, planted in past centuries and survived precisely thanks to the local climate conditions.

According to what the scientific sources put in writing, the first hypothesis is the most cited and the easiest to tell, but it must be presented as a hypothesis and not as an established fact. Whoever tells you with absolute certainty that those birches saw the ice age is selling a story, not a datum. This takes nothing away from the beauty of the wood, nor from its conservation value.

When the birches of the Caldara di Manziana are at their best

Late October and November. The leaves turn yellow and the contrast with the white trunks and with the pale floor of the basin produces the strongest sight of the year. In spring the birch grove is a tender green that lasts a few weeks. In high summer, with the vertical light, it gives much less.

The peat bog of the Caldara di Manziana

The third environment is the least spectacular and the rarest. The shape of the basin constitutes an ideal context for the formation of peat: the central depression collects rainwater, the impermeable muds on the bottom hold it, and the water level stays low and stable.

How peat is born

In this environment the vegetation growing on the ground, typically grasses and sedges, progressively decomposes and accumulates on the ground, while new growth rises above. The shallow depth of the water and the lack of oxygen inhibit the activity of decomposing bacteria and favor chemical processes that progressively enrich the buried plant material with carbon. This is how peat is born. It is a process so slow that it puts any hurry in perspective: peat accumulates at the rate of a few millimeters a year.

Why a peat bog is worth a trip

Italian peat bogs are few, almost all alpine, and almost all in retreat. Having one an hour from Rome, inside a protected area, is a circumstance that ecologists consider a small treasure. Peat bogs are also archives: the pollen deposited in them is preserved in the layers and allows the reconstruction of the vegetation history of a territory. When you walk on the edge of the Caldara di Manziana you are skirting a book of climate history still being written.

The wet meadow and the rare plants of the Caldara di Manziana

From the floristic and vegetational point of view the site, besides the birch grove, is colonized by a wet meadow dominated by a very rare Italian grass, Agrostis canina subspecies monteluccii. The scientific name says nothing to the ordinary visitor, and visually it is a low turf that to a distracted eye looks like any meadow. It is not: it is one of the reasons the Caldara di Manziana appears in the Natura 2000 network.

Why you don't leave the trails

Here is the practical point that follows from botany. A wet meadow of rare species does not tolerate repeated trampling. Every shortcut traced by a visitor who cuts across to reach the spring sooner becomes a path, and every improvised path takes space away from the vegetation that the site was established to protect. Staying on the beaten paths at the Caldara di Manziana is not bureaucratic fussiness: it is the difference between a protected area and a worn-out meadow.

The name, the Etruscans and the god of the Underworld

The territory of Manziana and of Canale Monterano was consecrated by the Etruscans to the god of the afterlife Manth, in Latin Mantus. From that deity took its name the Silva Mantiana, the great wooded area that dominated the hills west of Lake Bracciano and of which the nearby Bosco Macchia Grande is the only sector that survives today. The name of the town, Manziana, descends in a direct line from that wood and that god.

Why an infernal god right here

The association between the forest and Manth derived with every probability from two concrete factors. The first is the look of the forest: dense, dark, impenetrable, the kind of wood that an ancient community considers the edge of the known world. The second is the widespread presence of sulfurous water springs, that is the Caldara di Manziana itself, and of the solfatara of Monterano: waters that boil without fire, vapors that stink of sulfur, ground that breathes. For the ancients all this was an emanation of the underground world, and the religious explanation came long before the geological one.

A reading that still holds

I find it one of the most honest interpretations of the relationship between landscape and ancient religion. No arbitrary myth: the Etruscans placed the door to the afterlife where the ground actually emitted gases deadly to animals that got too close. They were wrong about the cause and right about the effect. It is worth remembering while looking at the basin from the edge: that perception of a threshold, of a place that is not entirely earthly, is not a modern literary invention.

The muds, the legions and the flocks

The post-volcanic activity of the Caldara has drawn the attention of the local population since antiquity, for religious reasons and for the supposed healing effects of the waters and muds. Local tradition tells that Roman legions stopped at the Caldara to purify themselves after long military campaigns, before returning to the city. It must be said clearly that this is handed-down tradition, not a fact documented by ancient sources: it is a nice story, and as such should be told.

A use that lasted into the twentieth century

Much better attested, instead, is the use of the muds in modern times. The healing action of the muds was practiced on people and on animals, so much so that until the middle of the last century recurring baths were still given to flocks, herds and other domestic animals. It is a detail that says a lot about the agro-pastoral life of this corner of Lazio: the Caldara di Manziana was not a place for outings, it was a piece of working equipment, a collective therapeutic bath for the town's animals. This news is reported in the volume Giganti verdi. Percorsi culturali nella natura 4 Manziana.

And not today

Today those baths are no longer done, neither for animals nor even less for people. The Caldara di Manziana is a protected area and an active degassing site: immersion is forbidden and dangerous. Whoever arrives with the idea of a free natural spa has the wrong address and risks a lot.

The protection of the Caldara di Manziana

The history of the protection of this place proceeds by successive layers, like the ground it protects.

From natural monument to Special Area of Conservation

The area was originally protected as a natural monument, the formula that regional law reserves for sites of limited size and exceptional value. At a second stage it was included in the Bracciano-Martignano Regional Natural Park, established by the Lazio Region with the regional law of November 25, 1999. On July 19, 2006 the European Commission, with decision 2006/613/EC, adopted the area of the Caldara di Manziana as a site of Community importance for the Mediterranean biogeographic region with the code IT6030009. Today the site is classified as a Special Area of Conservation, measures 90.42 hectares, and is managed by the Ente Parco Bracciano-Martignano.

The conservation measures

The conservation measures of the Special Area of Conservation were adopted with resolution of the Lazio Regional Council no. 159 of April 14, 2016, while the managing body was identified with resolution no. 305 of June 19, 2018. Translated for the visitor: there are written rules on what can and cannot be done inside that perimeter, and they do not depend on the common sense of the moment. Whoever organizes a structured activity in the area, a commercial guided visit, a video shoot, an event, must contact the Ente Parco.

The Bracciano-Martignano Park around the Caldara di Manziana

The Bracciano-Martignano Regional Natural Park covers 16,682 hectares straddling the provinces of Rome and Viterbo and includes 10 municipalities: Anguillara Sabazia, Bassano Romano, Bracciano, Campagnano di Roma, Manziana, Monterosi, Oriolo Romano, Rome, Sutri and Trevignano Romano. The two volcanic lakes, Bracciano and Martignano, alone cover about 6,000 hectares, that is around 40 percent of the protected surface. Lake Bracciano, among other things, is a strategic water reserve for Rome in emergencies.

What ties the Caldara to the rest of the park

The Caldara di Manziana is not an isolated episode: it is the last visible manifestation of the activity of a volcanic district that dug the two lake basins, raised the hills and deposited the tuffs on which the Etruscans later carved their tombs. The marshy environment of the Caldara is what remains of the late activity of Sabatini volcanism, placed between about 600,000 and 40,000 years ago. Looking at the basin and then looking at the lake from the shore at Trevignano Romano means reading two pages of the same book.

The headquarters and contacts

The Ente Parco is headquartered at Via Aurelio Saffi 4/a in Bracciano, a few minutes from the train station, and answers at the number 06 99801176. It is the reference for environmental education activities, for guided visits organized by the park and for any authorization concerning the protected area.

The Bosco Macchia Grande of Manziana and the trail to the Caldara

The Bosco Macchia Grande of Manziana is the natural complement to the visit to the Caldara, and in many ways its most beautiful entrance. It is the last surviving fragment of the Silva Mantiana, a majestic Turkey oak wood with large specimens, managed by the Università Agraria of Manziana, an institution founded in 1904 that administers the agro-silvo-pastoral heritage of civic use belonging to the community of Manziana. The wood is classified as a Special Area of Conservation with the code IT6030008 and an area of 801.33 hectares.

CAI trail 262B

The official route that connects the Bosco Macchia Grande of Manziana to the Caldara di Manziana Natural Monument is CAI trail 262B. It measures about 5.5 kilometers, which become about 6.5 including the wooded stretch, is classified as an easy hiking itinerary and has a surface mostly of packed earth with about 200 meters of asphalt. You start from the main entrance of Macchia Grande, follow the Fontanili route to an iron gate and from there continue on the marked track 262b to the rest area of the Caldara. The vertical and horizontal signage of the Club Alpino Italiano is complete, and the GPX track is available to download on the Park's website.

Watch out for who shares the trail

The 262B is a route shared among hikers on foot, cyclists and horses. Those coming down on a mountain bike must proceed with caution, especially on the downhill stretches. Those on foot should expect that they may find a horse in front of them at a blind curve: you let it pass, you stay still, you don't shout. These are good manners that avoid serious accidents in these woods.

The long variant toward Bracciano

Whoever has the legs and time can extend onto CAI trail 262, which connects Manziana to Bracciano passing through the Pisciarelli, about three kilometers of medium difficulty, or onto the 262A, which adds the Archi di Boccalupo for a total of around seven and a half kilometers. These are tracks that let you build a full day starting and returning by train, without a car.

How to get to the Caldara di Manziana from Rome

Manziana is northwest of Rome, on the western slope of the Sabatini Mountains. You get there by two main roads and in two ways.

By car to the Caldara di Manziana

The most direct route for those leaving the capital is Via Aurelia heading north to Cerveteri and Furbara, then the inland climb toward Manziana along Provincial Road 2c. Alternatively you go up Via Braccianese to Bracciano and continue to Manziana. Once on SP 2c, which connects Manziana to Furbara station, about five kilometers from the town you meet Via della Caldara: you turn left and continue for about 500 meters along a dirt road to a small parking lot where you can leave the car. The parking lot is truly small: on spring and autumn weekends it fills up by late morning. Whoever arrives at 11 on a November Sunday leaves the car along the road, with all the nuisances that implies.

By train and on foot

The option I prefer, and the one I recommend to those who want to turn the visit into a real day, is the train. You get off at Manziana-Canale Monterano station, on the Rome-Capranica-Viterbo regional railway, and reach the Caldara on foot through the trails of the Bosco Macchia Grande: it is about seven kilometers from the station, on easy and marked routes. You walk inside a monumental Turkey oak wood instead of inside a car cabin, you avoid the parking problem and you arrive at the basin at the right pace. Check the regional train times before leaving and calculate the return time: on the short winter days darkness in a wood arrives sooner than you imagine.

The road surface and the right vehicle

The last 500 meters are dirt. A small car passes without difficulty when the ground is dry. After days of rain you meet puddles and ruts, and it's best to proceed at walking pace. No special vehicle is needed, but a low city car suffers.

When to visit the Caldara di Manziana

The season completely changes the experience, more than at almost any other natural site in Lazio.

Autumn, the best season

From mid-October to late November the birches turn yellow, the wood around shifts to browns, the air is moving and the days are very clear. It is the moment when the Caldara di Manziana gives back the most, both to the eye and to the camera. Go early in the morning, with the sun still low.

Spring

April and May bring the wet meadow to its peak vitality and the wood to its new green. The risk is mud: after a week of rain the trails around the basin become heavy and hiking boots are not a whim.

Summer, the season to avoid

I'll be blunt: the Caldara di Manziana in summer isn't worth the trip, and in certain conditions it is the least prudent season. The overhead light flattens the colors, the basin has no shade, the smell of sulfur at 40 degrees becomes oppressive and the days of still air are those in which the gas stagnates the most. If you really go in July or August, go at eight in the morning and stay on the high edge.

Winter

With the cold and clear air the bubbles are easy to see, the steam rising from the springs is more visible and the bare birch grove has a dry elegance of its own. The ground, however, is almost always wet. Short day, early start, return before 16:00.

The Caldara di Manziana with children

A frequent question, which deserves a double answer. Yes, the Caldara di Manziana is a place that fascinates children more than 10 museums put together: the water that boils by itself, the rotten egg stink, the white wood, the floor that looks like another planet. The park periodically organizes activities for families right at this site.

The non-negotiable conditions

And yet: hand in hand from the parking lot on, always. No running toward the water, no playing on the ground inside the basin, no lying on the meadow below. A five-year-old has their head a meter from the ground, that is in the band where carbon dioxide concentrates if the air doesn't mix. If you don't feel up to guaranteeing that control, take the walk in the Bosco Macchia Grande and look at the basin from above: the outing stays beautiful and the risk drops to zero.

The dog at the Caldara di Manziana

Short leash, no exceptions, and take care not to let it drink the marsh water. A dog follows its sense of smell and its sense of smell takes it exactly where it must not go. Many experienced visitors prefer to leave the dog at home when the day is still and muggy: it's a choice I share.

Accessibility and gear for the Caldara di Manziana

There are no routes equipped for wheelchairs: the ground is natural, irregular, often muddy, and the last access stretch is dirt. An accompanied trekking wheelchair can reach the edge of the area on dry days, but the basin is not passable. There are no restrooms, no bar, no refreshment point, no drinking water: you bring everything from home and take everything back home, trash included.

What to put in your backpack

Closed shoes with a lugged sole, never sandals. Water, at least a liter per person. A change of socks if you expect wet ground. Hat and sunscreen from May to September, because the basin offers no shelter. A windbreaker for winter. And a banal recommendation that nobody follows: metal objects and silver jewelry oxidize with prolonged contact with hydrogen sulfide, so leave them in the car if you care about them.

How long the visit takes

The basin alone takes 40 minutes, an hour if you stop to look and photograph. With the trail from the Bosco Macchia Grande the day rises to four or five hours including stops. Whoever arrives by train should count six full hours between outbound, walking and return.

What to see around the Caldara di Manziana

The Caldara alone doesn't fill a day. The surrounding territory, instead, fills three.

The lakes and the villages of the park

A few kilometers away open Lake Bracciano and the smaller Lake Martignano, reachable only on foot or by shuttle and for that reason left intact. On the large lake face Bracciano with the Odescalchi Castle, Trevignano Romano with its lakefront and Anguillara Sabazia with the village dropping sheer to the water.

The ghost village and the ancient woods

A quarter of an hour by car you reach Monterano, the abandoned village with its solfatara, its Bernini ruins and the landscape that served as the set for dozens of films. A little farther north the beech forest of Oriolo Romano on Monte Raschio, recognized as a World Heritage ancient beech forest, and the Mola di Oriolo Romano.

Toward the sea

Going down toward the coast you meet Cerveteri with the Banditaccia Necropolis, the Cascatelle del Fosso del Norcino, the Macchiatonda Nature Reserve and the Santa Severa beach with the castle on the sea, next to which is the Oasi naturista Le Sabbie Nere.

A well-built day

Frequently asked questions about Caldara di Manziana (RM)

How much does it cost to enter the Caldara di Manziana?

Access to the Caldara di Manziana is open and free: there is no ticket office and you don't pay for parking in the dirt lot. Any guided activities organized by the Ente Parco may have a cost and require booking, and the conditions should be asked directly of the Bracciano-Martignano Park.

What do you really see at the Caldara di Manziana?

The Caldara di Manziana is a basin of volcanic origin of about 90 hectares, occupied at the center by a marsh of sulfurous waters where the water bubbles without being hot, pushed by the carbon dioxide emissions that rise from below. Around it grow a grove of white birches and a wet meadow with rare plants.

Is the water of the Caldara di Manziana hot?

No, and this is the most common misunderstanding: the name caldara suggests water that boils because it is hot, but the mineralized spring of the Caldara di Manziana bubbles because of the gas emissions rising from the subsoil, not because of temperature. Many visitors reach out a hand expecting to pull it back sharply, and are surprised.

Is the Caldara di Manziana dangerous to visit?

The floor of the basin of the Caldara di Manziana emits a continuous flow of gas, made up mostly of carbon dioxide and, in smaller amounts, of hydrogen sulfide and methane. Hydrogen sulfide is the one you smell, the rotten egg odor that accompanies the visitor from the parking lot on, and it is precisely its perceptibility that makes it relatively less insidious than other gases present.

Is the Caldara di Manziana suitable for children?

Yes, the Caldara di Manziana fascinates children with the water that boils by itself, the wood of white birches and the floor that looks like another planet, and the park periodically organizes activities for families at this site. The safety conditions tied to the gas emissions must be respected, however, and you don't leave the indicated paths.

Is the Caldara di Manziana accessible in a wheelchair?

No, there are no routes equipped for wheelchairs at the Caldara di Manziana: the ground is natural, irregular, often muddy, and the last access stretch is dirt. An accompanied trekking wheelchair can reach the edge of the area on dry days, but the basin itself is not passable.

When is the best time to visit the Caldara di Manziana?

From mid-October to late November the birches of the Caldara di Manziana turn yellow, the wood around shifts to browns and the days are clear: it is the season when the place gives back the most, both to the eye and to the camera. It's best to go early in the morning, with the sun still low.

The best itinerary for a group: leave Rome at eight, Caldara di Manziana by 10 with the sun still low, walk in the Bosco Macchia Grande until one, lunch in Manziana or Bracciano, afternoon at Monterano or on the lakefront of Trevignano, return at sunset. Whoever prefers to rely on a professional for the organizational side can turn to the tour leaders of TourLeaderPro, who work on itineraries outside Rome of this kind.

A curiosity about Caldara di Manziana (RM)

The nicest curiosity of this place is that its name tells a lie, and has told it for centuries. Callara, caldara, caldaia: all the local vocabulary describes a vessel that boils. Whoever arrives at the edge and sees the water rise in bubbles, move, mutter, naturally concludes that the water is hot. Many visitors reach out a hand expecting to pull it back sharply. Instead the mineralized spring of the Caldara di Manziana has a temperature of about 20 degrees Celsius: lukewarm in January, cool in August, anyway very far from boiling.

The movement is not due to heat but to pressure. From the subsoil rise gas flows coming from depths of more than 2,000 meters, made up 98-99 percent of carbon dioxide. Those flows cross the layer of water held by the impermeable muds and make it bubble exactly as a straw blown into a glass would. It is a phenomenon of secondary volcanism, not of active volcanism: no magma chamber under your feet, no eruptive risk, only deep carbonate rocks that at temperatures above 200 degrees release carbon dioxide and push it upward.

There is a second curiosity inside the first, and it concerns the paradox of the temperature. Precisely because the water is not hot, the Caldara di Manziana could never become a spa establishment like so many other Lazio sites. Nobody built pools, nobody built hotels, nobody fenced it off and put in a ticket booth. The deception of the name ended up protecting the place better than any law: if the water had been at 40 degrees, today in place of the peat bog there would be a paved parking lot and a lobby with tiles. The fact that the Caldara has reached us with its birches and its wet meadow intact is also due to this fortunate misunderstanding.

Something nobody tells you about Caldara di Manziana (RM)

What almost nobody explains, and which should instead be written at the entrance in capital letters, is that the danger of the Caldara di Manziana is not the one you smell, but the one you don't smell. The rotten egg odor that greets the visitor comes from hydrogen sulfide, which when it reaches the surface oxidizes, releasing hydrogen ions and sulfur oxides. It is unpleasant, it is intrusive, and for that reason relatively honest: it warns of its own presence. The dominant gas, however, is another. Carbon dioxide makes up 98-99 percent of the emissions and is odorless, colorless and tasteless. It warns of nothing.

The second part of the information is elementary physics and changes everything: carbon dioxide is denser than air. It doesn't rise, it sinks. It collects in depressions of the ground, in pits, hollows, ditches, in low points sheltered from the wind, and stays there until a current of air mixes it. It follows that within the same area, at the same moment, the air breathed by an adult standing and the air breathed by a child sitting or a dog with its muzzle on the ground can be two different things. This is the technical, not moralistic, reason why at a degassing site you don't lie down, you don't go down into the basins, you don't let children play on the ground, and dogs are kept on a leash.

Third part: weather conditions matter more than the time of day. With strong wind and moving air the gases disperse quickly and the risk is minimal. With still air, high humidity, low haze and thermal inversion, dispersion slows. Nobody will hand you a bulletin at the entrance, because it doesn't exist. You have to apply the criterion yourself, by looking at the trees: if the leaves aren't moving and the air is heavy, that is the day when the Caldara di Manziana is looked at from the high edge and that's it. No photograph is worth feeling ill a kilometer from the paved road.

The advice I give you for visiting Caldara di Manziana (RM)

The advice is only one, and it is counterintuitive: do not drive all the way to the Caldara's parking lot. Leave the car in Manziana, or better still get off at Manziana-Canale Monterano station, and enter the Caldara from the wood, on foot. CAI trail 262B connects the Bosco Macchia Grande of Manziana to the Caldara di Manziana Natural Monument over about 5.5 kilometers of easy hiking route, almost all on packed earth, with complete Club Alpino Italiano signage and a GPX track downloadable from the Park's website.

The reason is not sporting, it is about understanding. Whoever arrives by car gets out of the parking lot, walks 200 meters, looks over the basin, photographs the bubbles, goes back and leaves convinced that the Caldara di Manziana is a 15-minute curiosity. Whoever arrives on foot first crosses the monumental Turkey oak wood, the last fragment of the Silva Mantiana, with large oaks and dense undergrowth. Then you feel the wood change. Then you begin to smell the sulfur long before seeing anything. And finally you emerge onto the pale clearing. In that order, the place explains itself. The transition from the dark green of the wood to the yellowish white of the basin is the geological and mythological story of this place staged by the ground.

Second advice, minor but practical: go early. Before 10 in the morning you find parking, raking light, silence and nobody shouting. After noon, on October and November weekends, the small parking area is full and the trail becomes a queue. Third advice: allow two hours, not 30 minutes. The Caldara is something you observe, and observing takes still time. Sit on the high edge, in silence, and count the springs: you will count more than you had seen on arriving.

Another well-known fact, yet rarely cited

That there is a birch grove at the Caldara di Manziana everyone knows, and it is the datum that appears in every list of unusual places near Rome. What is cited much less is that the origin of that grove is not at all established, and that on the question there are two openly competing hypotheses.

The first, the one told most often and almost always as if it were a fact, holds that the local conditions of the Caldara, with its permanent swamp and the humidity of the floor, created a microclimate favorable to the white birch, allowing the survival of a relic population from a period after the glaciations. In this reading the birch grove of the Caldara di Manziana is a fragment of cold flora left trapped at 250 meters of elevation while all around the climate warmed.

The second hypothesis is less romantic and should not be discarded: the grove could be of artificial origin, planted in the area in past centuries and survived precisely thanks to the favorable local climate conditions. A human planting, in short, that found the one spot in Lazio where it could hold.

The difference is not academic. If the birch grove is a glacial relic, the Caldara di Manziana is a biological archive of exceptional value and must be protected as such. If it is a historical planting, it remains a botanical and landscape rarity, but the scientific meaning changes. The available sources record both hypotheses without deciding. The correct way to tell about this wood, therefore, is in the conditional: and whoever accompanies you telling you confidently that those birches saw the ice is telling you the version that pleases most, not the one that can be proven. Prudence, here, is the highest form of respect for the place.

The right photo to take at Caldara di Manziana (RM)

The photograph everyone tries to take at the Caldara di Manziana is the close-up of the bursting bubble. It is also the worst: close, without context, indistinguishable from a pot of water, and to get it you have to approach the spring more than is prudent. Forget it.

The right photo is another, and is taken from the high edge of the basin, possibly from the side bordering the birch grove. You need the raking light of early morning or that of the hour before sunset, and you need to frame three superimposed bands: at the bottom the yellowish white floor of the marsh with the milky water, in the middle the pale band of the birch trunks, at the top the dark crown of the Turkey oak wood. Three colors, three climates, three environments in a single frame: that is the Caldara di Manziana, and it is an image that no other place in Lazio can give back.

Wait for the right moment and include a person seen from behind on the edge, small: it gives the scale of the basin, which otherwise is lost entirely in a photograph. If you have a telephoto lens, compress the planes from the opposite side: the birch grove becomes a white vertical barrier and the Nordic effect is accentuated.

Two technical warnings. The first: the steam rising from the springs reads well only in backlight early in the morning on cold days. At summer noon you see absolutely nothing and the photo is flat. The second: hydrogen sulfide is not good for metal contacts and silver parts, and the sulfurous humidity gets in wherever it can. Whoever brings serious equipment to the Caldara di Manziana keeps it in the backpack until the shot and cleans it at home. In autumn, with the birch grove yellow and the floor pale, this place gives the best nature photographs an hour from Rome.

Some important events that happened here in history

The history of the Caldara di Manziana is not measured in battles but in layers, and the documentable passages are more interesting than the legends.

The first event is geological and is the one that made everything else: the late activity of Sabatini volcanism, datable between about 600,000 and 40,000 years ago, which shaped this sector of the Monti Sabatini and left as a legacy the gas-rise system that is still active. Without that phase, no basin, no pools, no impermeable clays and no peat bog.

The second step is religious and cultural. In the Etruscan age the territory of Manziana and Canale Monterano appears consecrated to the god of the underworld Manth, Latinized as Mantus, and from that divinity takes its name the Silva Mantiana, the forest that dominated the hills west of Lake Bracciano. The association between the woodland and the god of the Underworld derived most probably from the gloomy, impenetrable look of the forest and from the widespread presence of pools of sulfurous water, the Caldara itself, and of the solfatara of Monterano, interpreted as emanations of the underground world.

The third chapter is that of therapeutic use. The post-volcanic activity of the Caldara has drawn the attention of the local population since antiquity for religious reasons and for the healing effects attributed to the waters and muds. Tradition has it that Roman legions stopped here to purify themselves on returning from military campaigns: this is a handed-down tradition, not a documented fact, and it must be said. Far more solid is the use in the modern age, continued until the middle of the 20th century, when at the Caldara di Manziana recurring baths were given to flocks, herds and the other domestic animals of the territory.

The fourth event is administrative and very recent, and it saved the site. The area, originally protected as a natural monument, is included in the Bracciano-Martignano Regional Natural Park established by the Lazio Region with the regional law of November 25, 1999. On July 19, 2006 the European Commission, with decision 2006/613/EC, adopts the Caldara di Manziana as a site of Community importance for the Mediterranean biogeographic region with the code IT6030009. The conservation measures of the Special Area of Conservation follow, adopted with resolution no. 159 of the Lazio Regional Government of April 14, 2016, and the identification of the managing body with resolution no. 305 of June 19, 2018. They are dates from a government office, devoid of any epic quality, and they are the reason why today birches still grow on the rim of this basin instead of a residential complex rising there.

Who has passed through Caldara di Manziana (RM)

The oldest visitor to the Caldara di Manziana that we have a trace of is not a person but a people. The Etruscans frequented this sector of the Sabatini and placed here the cult of Manth, the god of the underworld: the Silva Mantiana takes its name from him, and the woods together with the sulfurous waters were read as a door to the underground world. Whoever passed through here in the Etruscan age was not passing out of naturalist curiosity.

Of the Romans it is told, by local tradition and not by document, that the legions stopped at the Caldara to purify themselves after long military campaigns, before returning to the capital. Caution is required: it's a handed-down report, not an ancient source read. It does count, however, as a sign of continued use of the site, which modern documents confirm in another form.

The most certain protagonists, and the largest in number, are the people of Manziana themselves. For centuries the shepherds and farmers of Manziana brought flocks and herds here for therapeutic mud baths, a practice continued until the middle of the last century. And for centuries the community managed the surrounding woods through civic use, today administered by the Università Agraria di Manziana, an institution founded in 1904 that has in its care the agro-silvo-pastoral estate held in collective ownership. The history of this place is made in very large part of people who worked here.

In the 20th century the filmmakers arrived. The woods and farmhouses of the territory of Manziana, beginning with the farmhouse on Via delle Pietrische pointed out by the Università Agraria itself, served as sets for Italian productions of different genres: the closeness to Rome, the variety of the landscape and the absence of modern signs made this countryside a convenient and credible backdrop for decades. The lunar floor of the Caldara di Manziana, with its yellowish white and its water fumaroles, is exactly the kind of place a director of photography looks for when he needs an elsewhere.

Today it is visited by hikers, nature photographers, students on school trips, researchers studying degassing and Roman families on weekends. The Bracciano-Martignano Park periodically organizes environmental education activities there, including treasure hunts designed for the little ones. From gateway to the underworld to destination for a trip with children: few transformations are more radical, and few are more deserved.

Quick questions about Caldara di Manziana

How much does it cost to enter the Caldara di Manziana?

Nothing. Access to the Caldara di Manziana Natural Monument is free and open, there is no ticket office and you don't pay for parking in the dirt parking area. Any guided activities organized by the Park Authority may have a cost and require a reservation: ask the Park directly for the conditions.

Do you need to book to visit the Caldara di Manziana?

For a free visit, no. Booking is needed only for activities organized by the Ente Parco Bracciano-Martignano or for guided visits of structured groups, which in any case must be authorized.

Is the water of the Caldara di Manziana hot?

No, and it is the most widespread misunderstanding. The mineralized spring has a temperature of about 20 degrees Celsius. The bubbling is produced by the rise of gases, not by heat.

Can you swim at the Caldara di Manziana?

No. Immersion is forbidden and dangerous: the water is crossed by gas emissions and the floor is muddy and unstable. There are no pools, no establishment, no assistance.

Are the gases of the Caldara di Manziana dangerous?

They can be. The emissions are made up 98-99 percent of carbon dioxide, an odorless gas heavier than air that tends to accumulate in depressions of the ground, with a smaller fraction of hydrogen sulfide and methane. For this reason you don't go down into the basin, you don't lie on the ground, you don't let children play on the ground and dogs stay on a leash.

Is the Caldara di Manziana suitable for children?

Yes, provided they always stay hand in hand and on the beaten paths, without approaching the springs and without getting down on the ground. A child breathes lower than an adult, so closer to the layer where the gas can stagnate.

Can you bring dogs to the Caldara di Manziana?

Yes, on a short leash and never letting them drink the marsh water or sniff the ground for long inside the basin. On muggy days without wind it is more prudent to leave them at home.

Why does the Caldara di Manziana smell like rotten eggs?

The odor comes from hydrogen sulfide which, reaching the surface, oxidizes releasing hydrogen ions and sulfur oxides. It is the same odor as many thermal localities in the area. It stays on your clothes for a few hours.

How long does the visit to the Caldara di Manziana take?

From 40 minutes to an hour for the basin alone, arriving by car. Four or five hours if you arrive on foot from the Bosco Macchia Grande along CAI trail 262B.

How do you get to the Caldara di Manziana by car?

You take Provincial Road 2c that connects Manziana to Furbara station on Via Aurelia. About five kilometers from Manziana you turn onto Via della Caldara on the left and continue for 500 meters of dirt road to the small parking lot.

Can you reach the Caldara di Manziana by public transport?

Yes, by train to Manziana-Canale Monterano station on the Rome-Capranica-Viterbo regional line, then continuing on foot for about seven kilometers through the trails of the Bosco Macchia Grande. Times should be checked on the railway carrier's website before leaving.

How long is the trail from the Bosco Macchia Grande to the Caldara di Manziana?

CAI trail 262B measures about 5.5 kilometers, which rise to about 6.5 including the wooded stretch. It is classified as an easy hiking route, with a surface mostly of packed earth and about 200 meters of asphalt.

Can the trail to the Caldara di Manziana be done by mountain bike?

Yes, the 262B is also open to cyclists and horses, but it is a shared route: those coming down by bike must proceed with caution, especially on the downhill stretches, so as not to create risks for those on foot.

When is the best time to visit the Caldara di Manziana?

Autumn, between mid-October and late November, when the birches turn yellow and the air is clear. Spring is also good. Summer is the least suitable season because of light, smell and stagnation of the air.

Are there restrooms and refreshment points at the Caldara di Manziana?

No. There are no restrooms, bar, fountains or refreshment points. Water and food are brought from home and trash is taken back.

Is the Caldara di Manziana accessible in a wheelchair?

No, there are no equipped routes: the ground is natural and irregular and the final access is on dirt. On dry days an accompanied trekking wheelchair can get close to the edge of the area, but the basin is not passable.

How big is the Caldara di Manziana?

The Special Area of Conservation has an area of 90.42 hectares and the Natura 2000 code IT6030009.

Why are there birches at the Caldara di Manziana?

It is not established. One hypothesis considers them a cold-climate relic that survived thanks to the humid microclimate of the basin. Another holds them to be of artificial origin, planted in past centuries and survived because of favorable local conditions.

What is the peat bog of the Caldara di Manziana?

It is the progressive accumulation of little-decomposed plant material in shallow, oxygen-poor water: grasses and sedges settle on the bottom and are enriched with carbon, forming peat. It is a rare environment at Lazio latitudes.

Who manages the Caldara di Manziana?

The Ente Parco Bracciano-Martignano, headquartered at Via Aurelio Saffi 4/a in Bracciano, telephone 06 99801176.

Is the Caldara di Manziana an active volcano?

No. It is a site of secondary volcanism: gas emissions that rise from great depth and interact with surface water, without eruptive activity. The true volcanic phase is the late one of the Sabatini district, between about 600,000 and 40,000 years ago.

Can you pick flowers, muds or samples at the Caldara di Manziana?

No. The site is a Special Area of Conservation with conservation measures approved by the Lazio Region: the vegetation is protected and the wet meadow hosts rare species such as Agrostis canina subspecies monteluccii.

What is the difference between the Caldara di Manziana and the solfatara of Monterano?

They are two manifestations of the same secondary volcanism, a few kilometers from each other. The Caldara is a marshy basin with bubbling springs and a birch grove. The solfatara of Monterano is tied to the landscape of the abandoned village and its nature reserve. Both were interpreted by the ancients as emanations of the underground world.

Can you visit the Caldara di Manziana with a guide?

Yes. The Ente Parco Bracciano-Martignano periodically organizes activities and excursions in the area, including initiatives for families. Whoever arrives from abroad and is preparing a tailor-made itinerary outside Rome can rely on professional operators such as TourLeaderPro, or consult the English guides of ItalyPlanner dedicated to Italian nature.

Is it worth coming all the way from Rome?

Yes, provided you build a day around it: Caldara di Manziana in the morning, Bosco Macchia Grande, lunch in town, afternoon at the lake or at Monterano. As an isolated 20-minute stop, no.

The verdict on the Caldara di Manziana

The Caldara di Manziana is the right place for those who say they have already seen everything around Rome. It isn't spectacular in the way an alpine panorama is: it is disorienting. You get there through a thoroughly Italian Turkey oak wood and emerge onto a pale clearing that looks stolen from an Atlantic island, with a birch grove on the edge and water that boils cold in the middle of a meadow of rare species. It is worth the trip for this gap, not for the size.

Two things, however, must be said before leaving. The first: it is an active geothermal site, not a picnic area. You stay on the trails, you don't go down into the basin, children are held by the hand and dogs stay on a leash, and on days of still air you settle for looking from above. The second: whoever goes by car for 20 minutes takes home a tenth of it. Go on foot from the wood, in autumn, early in the morning. Then tell me if I was wrong. To build the complete itinerary around the lake you can start from the page of the Bracciano-Martignano Park, and for those organizing group excursions outside Rome the professional reference is TourLeaderPro. Whoever is preparing a trip to Italy and reads English will find on ItalyPlanner the complete guide to things to do in Rome and the surrounding area.

Article written by the editorial team of TourLeaderPro, contact them for Private/Corporate/V.I.P. Tours and Experiences.

Planning a trip to Rome? The English guides to visit the city are on ItalyPlanner.com.