Amihari Onsen Sennyo no Yu

Amihari Onsen, located in Shizukuishi, Iwate District, Iwate Prefecture, sits on a highland roughly 880 meters above sea level on the southwestern foothills of Mt. Iwate, and is said to have a 1,300-year history. Sennyo no Yu is a mixed-gender open-air bath located within the grounds of Kyukamura Iwate Amihari Onsen resort, reached by walking about seven minutes up a mountain path beside a stream from the main building's entrance. It is said that the poet Kenji Miyazawa once bathed here, making it a hidden gem known only to a few. The bath itself is a single, rustic pool built from stacked stones, where bathers can soak while listening to the nearby stream and the Kame-daki waterfall. It is open only during the green season (typically mid-May to early November) and is closed in winter under snow.

The spring is classified as a sulfur spring. The source water gushes at a scorching 76.7 degrees Celsius from a fumarole field within the explosion crater of Mt. Inukura, and is carried roughly 2 kilometers by pipeline while being blended with mountain stream water. The pH is 4.1, weakly acidic, and the color of the water shifts with the seasons: a milky, bluish-white in summer and autumn when stream water is abundant, turning nearly clear and colorless in drier periods. Although the water is diluted with stream water, it is never heated, recirculated, or chlorinated, making it a genuine free-flowing bath straight from the source.

Changing huts are separated by gender, but there is only one bathing pool shared by all. There are no lockers or facilities for storing valuables, and a rental bathing dress is available for women who prefer not to bathe nude. Admission is 700 yen for elementary school age and above, payable at the front desk of Kyukamura Iwate Amihari Onsen. The bath is open from 10:00 to 15:00 (last entry 14:00) and closes in the event of rain.