Hotaru Onsen

Japan's highest onsenchi, at 1,800 m on the slopes of Mt. Shirane in Gunma. Strongly acidic milky-white sulfur waters (pH 2.5) from one of the country's most active geothermal fields, with rotenburo open to alpine views year-round.

Nine-area onsen group along the Yokoyu River. Shibu's nine outer baths, Edo-period townscape, and proximity to the snow monkeys of Jigokudani are the draws.

One of the three great onsen of Japan (Sanmeisen). Famously hot, acidic waters; the wooden yubatake in the town center funnels source water into cooling channels.

Snow-country ski resort village with 13 free public bathhouses (sotoyu) maintained by the residents themselves.