Ishizuka Ryokan

The water here turns a vivid emerald green, and that is the main reason most visitors come. Indoor baths and an open-air bath are available, with mixed bathing (konyoku, 混浴) and a separate women's rotenburo (露天風呂). The spring flows fresh without recirculation. The water is quite strong, so short soaks are the norm. The ryokan is a member of Nihon Hitou wo Mamoru Kai (日本秘湯を守る会), the association of remote hot springs, and opens only from mid-May to early November. The building is old but kept tidy, runs on self-generated power, and sits largely out of mobile range. A drinkable natural spring is available at the entrance.