What is the difference between the free and paid thermal baths in Maremma?

The difference is mainly the supervision and the facilities : the free thermal springs are natural pools, while the paid establishments offer a developed space and more services. At Saturnia, the Cascate del Mulino are accessible free of charge all year round; the water is around 37 °C. However, the ground can be slippery, there is no swimming supervision at the natural site and you must bring a towel, non-slip shoes and clothes to change into. Parking may be paid.

Nearby, the paid thermal park of Terme di Saturnia gives access to maintained pools, changing rooms, showers and lockers subject to availability; parking is included with admission. Expect rather several tens of euros for a day, depending on the package and the season: check the price before leaving. It's more convenient, but admission doesn't turn the bath into a medical treatment and doesn't replace travel insurance. For your health, limit immersions to about 20 minutes, drink water and get out if you feel unwell. In case of pregnancy, heart or circulatory problems, ask a doctor for advice before bathing.