Ancient sulfurous, hot springs bubble up all around Southern Tuscany, especially within an hour or so of the extinct volcano, the Monte Amiata. These at Petrioli, flow into natural “vasche” (pronounced vas-kay) or “pools” in the Farma river. Access is free. When you can’t stand the heat in the pools closest to the spring (43 degrees C or 109 degrees F), you move to those further away and eventually, drop down in the chilly water of the river. The springs are located on the E78 between Siena and Grosetto. There is a fancy spa close to these outdoor pools if you want a mud bath, massage or a less rustic pool experience. http://termepetriolo.it/en/index.php
Bagni Vignoni has had springs since ancient times. Along the Orcia River, near the Monte Amiata between Montalcino and Montepulciano, the town was built around these pools (still in the square but no longer operating).
Of the modern springs/spas in Bagni Vignoni, I like the huge Piscina del Sole (Swimming Pool of the Sun) that sits just below the medieval tower at Rocca Di Castiglione. The part of the pool near the spring are hottest (43-45 degrees C/ 109-113 F) and sections further out are cooler.
You can pay a day fee for the pool and lawn chairs, pictured below, (open to the public 10,00-17,00 Jan-March and Oct-Dec and 9,30-18,00 April-September with 13-14,00 lunch closure/ closed Thursday/ open June-Sept for nighttime bathing 21-24,00 Fri, Sat, Sun only) or stay at the Hotel Posta Marcucci (nothing to write home about), which owns the pool, and have longer hours of free access. Another option is to take out a day membership at the hotel for access to a modern locker rooms, showers and spa treatments. (The ones for public use at the pool are basic, but I generally use them.) http://www.hotelpostamarcucci.it/en/index_en.htm
Another option are the springs of Chianciano, just south of Montepulciano. You can swim in the hot spring pools and use the modern locker rooms for a day fee, but the water is not as hot as Petrioli or Bagni Vignoni (35 degrees C/95 F). To me, having hot water is more important than a new hairdryer. http://www.theia-ilbagnodeglietruschi.it
There are modern spa services being added (by 2015), but for now, the “cures” require a medical appointment and are of the traditional Italian…aimed at curing ailments more than general relaxation.http://www.termechianciano.it/index.php?page=default&id=2&lang=en
Near Siena, you can visit the Terme of Rappalano, but the water comes into the pool at only 39 degrees C (102 F) and then cools off…not warm enough for me on the cool day that I visited. http://www.termesangiovanni.it/it/index.html
