Kiyotsukan

Kiyotsukan sits right at Kiyotsukyo, a gorge in the Niigata mountains, and its baths lean into that setting. The indoor bath, Yakushi-no-yu (薬師の湯), is a simple sulfur spring with separate rooms for men and women, open to lodging guests at any hour. The outdoor bath sits over the gorge stream and is a private, reservation-only soak booked at check-in, drawing on two separate springs at different temperatures; in winter you can bathe in the falling snow. It's an 11-room ryokan that describes itself as unpretentious and no-frills, guests are welcomed at an irori hearth in the lobby before anything else. The bath's name has a story behind it: it's named for a Yakushi Nyorai statue tied to the Sengoku-era lord Uesugi Kenshin, and the innkeeper's family says they found the spring in 1968 after tracing a faint sulfur smell the statue seemed to point them toward. Kiyotsukan also belongs to Nihon Hitou wo Mamoru Kai (日本秘湯を守る会), an association of secluded hot-spring inns. There's no day-use bathing here, only overnight stays.