We found San Giovanni Hot Springs when we visited in July 2013 and it was an awesome discovery. The Borgo pool was closed during our visit so we adventured to anywhere on the map we could find "Terme" or thermal springs, and one day we discovered this local treasure.
The hot springs are on a limestone quarry and the water is saturated with lime and doesn't smell too much like sulfur. In the cooler pools the lime collects at the bottom and is squishy on your feet - people rub this on their skin for its healing properties. There are water falls that are awesome to sit under (feels like a massage).