Ryounkaku

Ryounkaku sits at around 1,280 meters in the Tokachidake range, the highest hot-spring inn in Hokkaido. Two springs feed the baths: an iron-rich source that runs the water a rusty brown, and a lower-temperature, slightly acidic spring known locally for how thoroughly it warms you despite feeling cool at first. Bathing is split across two indoor rooms, Ooiwa (大岩) and Koiwa (小岩), plus an outdoor rotenburo facing the Tokachidake peaks; the women's rotenburo is built around a small cave. The men's and women's sides swap through the day so overnight guests can try both, and the water runs straight from the springs rather than being recirculated. Day-use bathing is open alongside overnight stays, and there's a sauna. The inn belongs to the Hitou wo Mamoru Kai (秘湯を守る会), an association of Japan's traditional secret hot-spring inns, and it runs snowshoe and trekking tours from the lodge in winter.