Izumiya Ryokan

Izumiya has two gender-separate open-air baths off the same spring: a rustic cave-style bath for the men's side and a hinoki-wood pavilion bath for the women's, each with a small indoor bath alongside it. The water is lightly sulfurous and smooth on the skin, and reviewers describe it as silky and slow to cool, the kind you can soak in a long time without feeling chilled afterward. The ryokan sits far up the Abe River in Umegashima Onsen, a hot spring said to date to the Kofun period, reached by a long drive upriver that adds to the feeling of getting away from everything. It's small and old-fashioned, worn but kept clean, and meals of local river fish and mountain vegetables are served in a private dining room. Day-use bathing is available, though irregularly, so it's best to call ahead.