Bagni di Petriolo: Free 43°C hot springs on the Farma River
A chain of natural sulfur pools on the Farma River where water springs at 43°C and bathing is possible all year.
Hidden beneath a forested viaduct between Siena and Grosseto, Bagni di Petriolo is a chain of sulfur springs on the Farma River where water emerges from underground at 43°C and fills a series of natural pools that flow into the riverbed.
Located in the Ombrone valley between Monticiano and Civitella Paganico, about twenty minutes south of Siena, the site is reachable by a short path down through the woods from the roadside. Steam often rises from the pools in winter, and year‑round bathing is possible thanks to the spring’s constant temperature.
Warm pools, cold river and a centuries‑old ritual
What makes Bagni di Petriolo unique is how nature regulates the temperature: hot sulfur water fills the upper basins and gradually mixes with the cooler Farma River as it descends, so each pool offers slightly different warmth. Visitors often follow a long‑standing custom: warm up in the hot pool and then plunge into the cold river for an invigorating contrast.
The air around the springs carries a distinct sulfur scent, and white mineral deposits and the milky tint of the water give the pools an almost otherworldly look. There are no changing rooms or sanitary facilities at the natural pools, and parking along the road is free but fills quickly in summer, so early arrival or off‑season visits are recommended.
For those wanting more comforts, the Mercure Petriolo Siena Terme Spa hotel and the organized Terme di Petriolo complex lie nearby inside the Farma nature reserve. The Terme di Petriolo complex was closed from 4 July to 31 August 2026 and was announced to reopen on 1 September, allowing visitors to combine free riverside bathing with access to formal spa facilities and wellness services.
Bagni di Petriolo also has deep historical roots: the springs were known in Roman times and attracted figures such as Cicero, Pope Pius II and members of the Medici and Gonzaga families. In about 1404 local residents built defensive walls around the baths — remnants of those fortifications remain today, and some sources describe Petriolo as the only fortified thermal complex in Tuscany.
The site is roughly 30 kilometres from Siena, making it possible to spend a morning in the warm water amid silent woodland and then walk Siena’s medieval streets the same afternoon.
Photo: press material from the event
