Located at an altitude of approximately 700 meters in Manganji, Minamioguni, Aso District, Kumamoto Prefecture, Okyakuya is the oldest inn in Kurokawa Onsen. Founded in 1722 (Kyoho 7) with about 300 years of history, it originally served as an Okyakuya, a guesthouse for the Higo Hosokawa clan that protected the domain border, hosting feudal lords, officials, and samurai for lodging and therapeutic bathing. It is regarded as one of the birthplaces of Kurokawa Onsen and stands quietly along the Tanoharu River. The water is a sodium-chloride and sulfate spring, supplied directly from the inn''s own source as free-flowing onsen with no recirculation. The inn features open-air baths, indoor baths, and private baths, making it a central hub for Kurokawa''s renowned bath-hopping culture. The interior preserves Edo-period craftsmanship while offering modern comfort, providing a serene stay in the mountain village of Aso.