Kusatsu Onsen (草津温泉) is a hot spring resort located in Gunma Prefecture, Japan, northwest of Tokyo. It is a popular tourist destination. The source of its hot water is nearby Mount Kusatsu-Shirane. The springs were a well known resort for centuries but they became one of the best known of such locations after the water there was recommended for its health benefits by Erwin von Baelz a German doctor who taught medicine at Tokyo University. The locals claim the hot springs can cure all forms of ailments except love sickness. Guests have claimed that pain disappears while soaking in its hot water.