Yumata Onsen is a hidden hot spring (“hitō”) located in the Takase Gorge at Hirayumata, Ōmachi City, Nagano Prefecture, with views of Mt. Tsubakuro to the east. Along the way you’ll pass Seiransō, a mountain hut sitting at about 1,534 m on the slopes of the Northern Alps. Beyond Takase Dam, follow the Minamata River and suddenly you’ll see water bubbling up directly from the riverbed. The highlight is the “Funtōkyū,” a natural hot-spring deposit formation designated as a National Natural Monument.

The main facility, Seiransō, was built in 1958 (Shōwa 33). It has indoor baths separated by gender, a dining room, and flush toilets. The wild outdoor baths, however, have no facilities at all—completely untouched nature. They are only available during the hut’s open season (mid-July through mid-October).