Shintakayu Onsen Azumaya Ryokan

Azumaya Ryokan (吾妻屋旅館) is a lone inn tucked into the mountains above Yonezawa, open since the Meiji era and a member of the Nihon Hitou wo Mamoru Kai (日本秘湯を守る会), Japan's hidden-hot-spring preservation society. There are five outdoor baths, each with its own character: one looks out over the Iide mountain range, another is carved from the trunk of a 300-year-old chestnut tree, and a third sits beside a waterfall (accessible only from late May once the snow clears). The water runs milky and faintly sulfurous, fed kakenagashi straight from the spring. Most outdoor baths are mixed-gender (konyoku, 混浴), with a dedicated women-only bath and all outdoor baths reserved for women between 18:00 and 20:00. Indoor baths are for overnight guests only.