Iwakura Onsen

Iwakura Onsen is a single-inn hot spring in Yumoto, Nangai, Daisen City, Akita Prefecture, set in a quiet valley along a tributary of the Omono River. Records from 1647 already describe it as a therapeutic bathing site, and the Edo-period traveller Sugae Masumi mentioned it as Iwakura-no-yu in his writings. The source dried up after the 1914 Kowakubi earthquake and the inn closed, but drilling later restored the flow and the inn reopened in 1958. It is now a member of the Japan Association of Secluded Hot Spring Inns.

The water is a sodium-calcium chloride-sulfate spring, hypotonic, weakly alkaline and hot. The source emerges at 58.2 degrees Celsius with a pH of 6.74 and a yield of 700 litres per minute, giving a total mineral content of 4.38 g/kg. It is colourless, odourless and tasteless, and is served entirely free-flowing with no added water, no reheating, no recirculation and no chlorination. Guests have long reported unusually deep sleep after bathing, which is why the inn calls itself the Inn of Deep Sleep.

Bathing is in indoor baths only, one each for men and women, with an unusually deep tub of 85 cm. There is no open-air bath and no private bath. The inn has seven guest rooms and sleeps twenty, with a dining room and a spacious lobby. Day-trip bathing runs from 10:00 to 18:00 for 500 yen per adult, closed on Wednesdays. Free parking is available for twenty cars.