Free Natural Thermal Spring · Monte Amiata Forest · Year-Round
Fosso Bianco
The White Whale — a thermal waterfall in the forest, free to all
In the chestnut and oak forest above Bagni San Filippo, a thermal stream descends the hillside over a series of natural terraces it has built for itself over thousands of years. The water — at about 48°C — is saturated with calcium carbonate. As it cascades and pools, it deposits the calcium as brilliant white travertine, building formations of extraordinary beauty: rippling curtains of white stone, shallow pools edged in calcite, a slow-motion sculpture park with no architect. The locals call the largest formation "La Balena Bianca" — the White Whale. There is no entry fee. There is no ticket booth. There is only the steam rising from the trees.
The White Formations
How the Thermal Water Sculpts Stone
The Fosso Bianco is a living geology lesson. The thermal spring emerges from the volcanic rock of Monte Amiata at approximately 48°C. As the water cools and hits the air, the dissolved calcium carbonate precipitates out and deposits on any surface — stone, leaves, fallen branches, itself. Over centuries these deposits have built up into layered travertine terraces: pale, smooth, constantly changing. The shape of the formations shifts seasonally as the water finds new paths. The largest deposit — the "White Whale" — is a hulking white mass about 6 metres high. Swimming in the pools below it, in water that is just warm enough to be comfortable, is an experience unlike anything else in Tuscany.
How to Visit
Getting to the Fosso
The Fosso Bianco is reached by a short walk (15–20 minutes) from the village of Bagni San Filippo. Park in the village and follow the signs marked "Fosso Bianco" or "Terme Libere" into the forest. The path is unpaved and can be slippery — wear shoes you don't mind getting wet. The thermal pools are open at all times and free to use. In summer the site can become crowded between 11:00 and 16:00 — go early (before 9:00) or late (after 17:00) for the best experience. In winter the steam in the cold forest air creates an atmospheric, otherworldly scene.
Practical Information
- Location
- Above Bagni San Filippo, Castiglione d'Orcia (SI)
- GPS
- 42.8756° N, 11.5364° E (approx. — follow path signs)
- Walk from village
- 15–20 minutes on forest path (can be muddy)
- Water temperature
- Approximately 48°C at source; pools cooler
- Entry
- Completely free, all year, all hours
- Best time
- Early morning or late afternoon; winter for atmospheric fog and steam
- Bring
- Old shoes (you'll get wet), towel, water — no facilities on site
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