Shiobara Motoyu Onsen Hito no Yado Gensenkan

A remote inn deep in the Shiobara valley, Tochigi, with three distinct sulfur springs on site. The water ranges from milky white to pale green depending on which spring you use, all free-flowing. There's a riverside open-air bath, an indoor bath, and a mixed-gender one (women-only in the afternoons and evenings). Cats roam the lobby, and the location feels genuinely off the beaten path.