Tamagawa Onsen
The Tamagawa Onsen hot spring boasts Japan’s highest output of hot spring water, at 9,000 liters per minute. Its pH of 1.2 also makes it the hot spring with the highest acidity level in the country. First discovered in 1681, Tamagawa Onsen opened as a center for hot-spring therapy (toji) in 1884. In 1932, the first steps were taken toward developing Tamagawa Onsen as a full-fledged health resort. Its highly acidic therapeutic waters have drawn visitors from all over Japan ever since.
The Tamagawa Onsen Nature Research Path takes visitors on a 30-minute stroll around the grounds. The path leads to the gushing Obuki spring, the origin of Tamagawa Onsen, where water comes to the surface at 98°C. Vapor can be seen rising from the ground here and there along the path. Among the vents, rocks heated by geothermal energy become natural stone saunas, where people lie on mats to warm themselves from top to toe and soothe their muscles.