Susan and I went on a little road trip mostly in southern Tuscany. There is a lot of geothermal activity in this area creating many natural hot springs. Most of these sites have been turned into spas. We stopped at Bagni San Filippo where there are hot springs that haven’t been commercialized and you can just hop in. The white walls are built up with calcium carbonate that creates a sort of mud as it precipitates out of the water as it cools. The hot springs also release a little sulfur to keep your olfactory sense engaged.
John and Susan's Excellent Adventure 