Mashitomi Onsen Furō 閣

Masutomi is one of the richest radon springs in Japan, and Furokaku is the place to experience it properly. The prize bath is a natural rock pool carved from a boulder, a short walk up a mountain path from the inn, where bubbles rise from the floor and the water sits at around 30°C, warm enough to stay in for a long therapeutic soak. Mixed bathing in the rock bath is a brief window in the early evening (guests only). The inn draws serious regulars who come for the huji-style healing, not a weekend dip.