Terme di Petriolo

What to expect

Petriolo is one of the free hot springs of southern Tuscany, and one of the least dressed up. A spring of hot, sulphurous water rises on the north bank of the Farma, a small river in the hills between Siena and Grosseto, and runs down over the rocks into a row of shallow pools at the water’s edge. Low walls of river cobbles keep the hot water in and the cold river out. Over time the minerals have coated the rocks white, and the pebbles on the bottom carry a slippery grey sulphur mud that people smear on their skin.

The water comes out at 109°F43°C. The hotel that draws on the same spring describes it as salty and hyperthermal, with a strong smell of hydrogen sulphide (21 mg/l), and gives the flow as about 40 litres a second. The pools nearest the spring are properly hot. Lower down, nearer the river, visitors report something closer to 95-99°F35-37°C, and you can step out into the cold Farma to cool off between soaks.

Above the pools stand the thick stone walls and low arcade of the old spa. OpenStreetMap maps the walls, a small church and the free bathing area (marked as free of charge) side by side. There is nothing else: no changing rooms, no toilets, no lifeguard. Some visitors mention food vans on busy days.

This page covers the whole site. The free pools are the main reason to come, and the paid spa building and the hotel above are described below.

A medieval spa castle

The baths are old. The hotel cites a mention by Cicero and an epigram by Martial, and the first written records date from 1230. In the early 1400s Siena built a walled bath complex on the north bank of the Farma, in what is now the municipality of Monticiano. Travel writers call it a thermal castle, built to protect the spring and, according to one account, to charge visitors for using it. Pope Pius II came here in the Renaissance, as did members of the Medici and Gonzaga families. The walls you see above the pools are what remains.

Getting there

Petriolo sits right beside the SS223, the dual carriageway between Siena and Grosseto, on the border between the provinces of Siena and Grosseto. A 2024 guide puts it at about 33 km (21 miles) from Siena and 45 km (28 miles) from Grosseto, or roughly 30-45 minutes by car. Guides describe a free car park near the entrance, though visitors complain that it fills up quickly. OpenStreetMap marks the large car park by the spa building as for customers only.

From the parking area it is a short walk down to the river. The rocks around the pools are uneven and slippery, so water shoes help.

Without a car it is awkward. One guide suggests the train to Civitella Paganico station, about 20 km away, and a taxi from there. Another suggests a bus to Civitella Marittima and a taxi of about 15 km.

When to go

The free pools have no set hours, and guides say they are open day and night. Weekends and holidays get crowded, especially in summer and on long weekends when Italians head for the free springs. A weekday morning in the cooler months is the best bet: the air is cold, the pools steam, and you have more space.

In summer the hot water and the heat of the Tuscan afternoon are a lot together. Go early or late in the day.

Rules and etiquette

There is no operator at the free pools, so the rules are the usual ones for a free spring in Italy:

• Wear a swimsuit. This is a public place, not a clothing-optional spring.
• No soap or shampoo in the pools.
• Take your rubbish home. There are no bins.
• Do not move the stone walls. They hold the hot water in the pools.
• Do not leave valuables in the car.

The spa building and the hotel

Next to the free pools is the Terme di Petriolo spa building, which OpenStreetMap marks as a paid public bath. A 2024 guide described indoor and outdoor pools overlooking the river, inhalations, mud baths and massage, some covered by the national health service, open from about 9 a.m. to 5:30 p.m. A September 2026 report said it had reopened on September 1 after its summer break, with pool entry at €15 and no booking needed. Its old website domain has lapsed, so phone before going: the number given in 2024 was +39 0577 757104.

On the slope above, in the municipality of Civitella Paganico and inside the Basso Merse nature reserve, stands a spa hotel. Its website still uses the name Mercure Petriolo Siena Terme Spa, while some booking sites now list it as Petriolo SPA Resort UNA Esperienze. It takes the 109°F43°C water straight from the spring for its own spa: two thermal pools, two heated whirlpools, a sauna, a Turkish bath, a Kneipp path and showers.

Where to stay nearby

The hotel above the baths is the obvious choice if you want to stay on site. Otherwise, the hill towns of Monticiano and Civitella Paganico are close, and Siena is about 40 minutes away by road with a wide choice of hotels. Agriturismi are scattered through the surrounding hills.

Safety notes

• Hot water: the pools nearest the spring are close to 109°F43°C. Test with a hand, keep soaks short and get out if you feel dizzy.
• Untreated water: nobody tests or disinfects the free pools. Keep your head above the water and stay out with open cuts.
• Footing: the rocks are slick with mineral deposits and sulphur mud. Walk slowly, especially carrying children.
• The river: the Farma can rise fast after heavy rain. Stay out of the main channel when it is running high.
• Children: the free pools are fine for children with close supervision, but there is no lifeguard and the hottest pools are too hot for them.

Nearby stops worth adding

Southern Tuscany has several other free or cheap thermal stops. Fosso Bianco at Bagni San Filippo has white travertine pools in a wooded stream. The Cascate del Mulino at Saturnia is the famous free cascade in the Maremma. Antica Querciolaia at Rapolano Terme is a paid thermal park east of Siena.