Kakuma Onsen is a quiet therapeutic hot spring village located along the Kakuma River in Yamanouchi Town, Nagano Prefecture, forming part of the Yudanaka-Shibu Onsen area. Legend has it that the hot spring was discovered by Rennyo Shonin, a high priest of Jodo Shinshu Buddhism, during the Muromachi period. The area has been beloved by many literary figures and artists including Fumiko Hayashi, Eiji Yoshikawa, and Taikan Yokoyama, whose villa still remains here. Oyu is a large wooden bathhouse standing at the center of Kakuma Onsen, boasting the most dignified appearance among the three public baths (Oyu, Taki-no-Yu, and Nitta-no-Yu). The spring water is a sodium-chloride and sulfate spring (containing arsite gypsum and weak saline) with a source temperature of 87.8 degrees Celsius. The abundant hot water flows freely from the source. The spring has been featured on TV for its effectiveness against atopic dermatitis, attracting many visitors seeking therapeutic treatment. Access requires a special wooden key (marked Kakuma-gumi) borrowed from the accommodation. The water is hot with a seawater-like scent, initially tingling but leaving the skin feeling smooth and moisturized.