Semi Onsen Kishiro

Kishiro is a long-established inn standing alone at Semi Onsen, on the left bank of the Oguni River in Mogami Town, Yamagata Prefecture. Legend holds that the spring was discovered by Minamoto no Yoshitsune's party as they fled toward Hiraizumi, when the warrior monk Benkei found the hot water while searching the valley for a bath for Yoshitsune's infant son. The wooden inn is said to date from the Meiji era and its main building is counted among the oldest surviving inn architecture in Yamagata.

The water is a sodium chloride-sulfate spring, rising at about 66C with a pH around 7.4, placing it between neutral and mildly alkaline. The cloudy grayish-green water carries a faint mineral scent and is said to ease joint and nerve pain; it is served largely as free-flowing source water, tempered with adjustment water where the source runs too hot.

The inn's centerpiece is the Roman-style Sennin-buro, a circular bath about 5.5 meters across fed from a central pillar, used as a mixed bath with reserved hours for women. Other baths include the gender-separated Atatamari-yu, the Dutch Bath in the annex, a rock bath, and a traditional steam bath. Both overnight stays and day-trip bathing are available, with day-trip entry for 500 yen.