Yuya Onsen Sengakukan

Sengakukan is a small ryokan on a clear mountain stream in Yuya Onsen, Osaka Town, Gero City, Gifu Prefecture, about 30 km northeast of Gero Onsen. Yuya Onsen is a historic toji (therapeutic bathing) village said to have been discovered around 480 years ago, in the mid-Muromachi period, when an ailing samurai was led to the spring by Yakushi Nyorai, the Buddha of healing. The area is designated a National Recuperation Hot Spring Resort (Osaka Onsen-kyo) and is famed for some of Japan's rarest naturally carbonated springs. Sengakukan's family has guarded its private spring source for four generations.

The water is a simple carbon-dioxide cold mineral spring (hypotonic, mildly acidic), emerging at just 12.2 degrees Celsius with pH 5.6 and 1,203.8 mg/kg of free carbon dioxide, exceeding the 1,000 mg/kg therapeutic-spring threshold. After more than a decade of trials, the inn developed a unique heating technique that warms the cold spring without losing its carbonation, so bubbles still cling to your skin in the bath. The spring is also licensed for drinking and tastes like natural cider; it is used for spring-water coffee and carbonated-spring shabu-shabu.

The inn has only seven guest rooms, all renovated in 2026 with private open-air carbonated-spring baths. There are also gender-separated indoor baths and a free private open-air bath reservable at check-in (overnight guests only). Day-trip bathing is not offered. Rates start from 14,300 yen per person with two meals; check-in 15:00, check-out 10:00, plus 150 yen bathing tax.