There are lots of hot spring facilities in Japan. There even is a hot spring tourism offering tours with very popular leisure activities. Hot springs contain ions and minerals and there are believed to soothe and heal injures and diseases. That's one side of their benefits. And other is that of relaxation and mental healing. Spa therapy has been practiced since the ancient times, which is called toji. Nowadays, there are an increasing number of hot springs facilities even in the middle of the Tokyo Metropolitan district, which have gained popularity as theme parks. It is customary to enter a hot spring naked although exceptions to this custom can be made.