Kamasaki Onsen Mogamiya Ryokan is a historic therapeutic hot spring inn established in 1789, nestled in a quiet valley at the foot of the Zao Mountain Range in Shiroishi City, Miyagi Prefecture. Kamasaki Onsen was discovered in 1428 when a farmer struck the ground with the tip of a sickle (kama) and hot spring water gushed forth, giving the spring its name. Known as the Medicinal Hot Spring of Ou (Oshu no Yakuyu), the spring has approximately 600 years of history as a healing water. The sodium chloride-sulfate spring (pH 7.1, source temperature 36.1 degrees Celsius) is rich in iron, producing a distinctive light yellowish-brown cloudy water. It flows at 100% natural free-flow with no dilution, circulation, or disinfection (heating is applied as the source is lukewarm). The water is especially effective for cuts, burns, neuralgia, rheumatism, and post-surgery recovery, with warmth that persists long after bathing. The main building, constructed in the Taisho era (1912-1926), preserves the charm of traditional Japanese wooden architecture with its amber-polished staircase, and is registered with the Japanese Cultural Heritage Preservation Society. The inn offers two communal baths (Sanpo-no-Yu and Tokin-no-Yu) and a private ship-shaped bath (Wago-no-Yu), along with self-catering rooms for traditional toji (therapeutic long-stay) experiences. A member of the Japan Association of Secluded Hot Spring Inns. The feudal lord Date Masamune is said to have bathed here.