Sanbeso Onsen Hotel

Sanbeso is a kokumin-shukusha (国民宿舎, a national lodge) at the foot of Mount Sanbe, built around a bathhouse far bigger than the room count would suggest: sixteen tubs across the men's and women's sides, in cypress, ceramic, iron kettles, sake barrels, and even a boat shaped tub, split between indoor and open air. Two tubs at the back, a pair of sake barrels and a kettle, run straight from the source with no added heat, so they sit at natural spring temperature. The water is an iron bearing chloride spring that colors the tubs amber brown and leaves a faint iron taste and smell, and in the colder months it turns genuinely cool, which regulars use for a hot and cold circuit. There's also a cold plunge and a small sauna. People come here as much for a soak after hiking Mount Sanbe as for the baths themselves, and the annex has a private reservable open-air bath for anyone who wants the water to themselves.