Oyado Manyoutei is a prestigious ryokan located in the Nakanosawa Onsen area on the western slope of Mt. Adatara at approximately 800 meters elevation in Inawashiro-machi, Fukushima Prefecture. Originally established as a new wing of the Ogawaya Ryokan, which boasts over 130 years of history, it opened in 1991 and was renovated in 2016. Exclusively for guests aged 16 and above, it offers a refined adults-only retreat surrounded by serene mountain scenery. The inn is a member of the Japan Association of Secluded Hot Spring Inns (Nihon Hitou wo Mamoru Kai). The hot spring source is the Numajiri Motoyu near the Numanodaira crater of Mt. Adatara, which boasts Japan's largest natural hot spring output from a single source at approximately 14,200 liters per minute. The water is piped approximately 7 kilometers to the inn, resulting in a strongly acidic sulfur spring (pH 1.85) with virtually no sulfur odor and a silky smooth texture. The water is 100% free-flowing from the source with no dilution or heating. Known since ancient times as a medicinal spring beneficial for gastrointestinal health, the inn features cypress wood open-air baths, all-wood indoor baths, and private open-air baths with ceramic tubs. The cuisine featuring Aizu-grown Koshihikari rice and locally sourced ingredients is also highly acclaimed.