Andaikan

Andaikan is a wooden, three-story ryokan founded in 1902, the first inn you reach as you come into Andai Onsen along the Yokoyu River. It has two indoor baths: a small one with a hinoki tub and a tiled tub called Kodai-buro (古代風呂), and a curved, big-windowed bath called Ryugu-buro (竜宮風呂) where you can hear the spring water flowing in. The two baths swap between the men's and women's sides after dinner and again after breakfast, so guests get to try both. The kakenagashi (掛け流し) water feels smooth on the skin, and reviewers describe it as clear with fine mineral flecks. There's no day-use bathing here, the baths are for overnight guests only, but the retro building keeps old touches throughout and has a small library room stocked with manga.