Stuttgart is home to several naturally occurring mineral baths. My favorite is the DAS LEUZE Mineralbad, pictured here. It is my personal heaven in the summertime. There are several different indoor and outdoor pools, all at varying temperature levels. They also have a sauna, offer massages, and have a couple of restaurants. You can reach the mineral baths (there are others in the immediate area) by taking the U2 train line toward Neugereut and get off at the Mineralbader stop.