Yomogihira Onsen Izumiya

Izumiya is a ryokan in the Yomogihira valley southeast of Nagaoka, with a stream running below the baths. There are three large bathhouses, each with its own indoor and outdoor pool: Tsuki no Yu (月の湯) sits among big boulders with light filtering through the trees, Hoshi no Yu (星の湯) is wood-toned with a clear view over the mountains and its indoor bath adjoins a ganbanyoku (岩盤浴) rock-bed sauna split into three sections, and Kaze no Yu (風の湯) adds a reclining tub facing the same mountains. The spring itself is sulfur water, kept on the cool side on purpose so you can stay in longer, and it leaves skin feeling slick and smooth. Two private baths can be booked for a soak on your own: Hanagoyomi (花ごよみ), indoor with a flat threshold that works well for kids or anyone less steady on their feet, and Yamano (やま野), a bigger open-air tub with its own outdoor washing area. Day-use bathing without staying overnight is available too.