Otasshan-yu is a traditional public bathhouse in the heart of the Obama Onsen district, established in 1937. Obama Onsen boasts the highest thermal heat output in Japan, with source temperatures reaching 97 to over 100 degrees Celsius. Here, the scalding water is tempered with cold water and delivered as a free-flowing bath. The men's bath features a divided tub, with a hotter side near the inlet and a cooler side, allowing bathers to choose their preferred temperature. The bathhouse retains the atmosphere of the Showa era, kept immaculately clean despite its age, and serves as a cherished daily gathering place for local residents. At just 200 yen per visit, it is open from 6:00 in the morning until 21:00. The sodium chloride water is rich in salt minerals, providing excellent heat retention that keeps the body warm long after bathing. This is a little-known gem where visitors can experience the everyday hot spring culture of Obama Onsen.