Okunasu Onsen Omaru Onsen Ryokan

Omaru Onsen Ryokan is a single, secluded inn set deep in the Okunasu highlands at roughly 1,300 meters above sea level, in Yumoto, Nasu, Tochigi Prefecture. With more than two centuries of history, it was favored during the feudal era by the Ozeki family, lords of the Kurobane domain, and in the Meiji period it became a cherished retreat of General Nogi Maresuke and his wife. Photographs and letters connected to the general are still preserved at the inn. Sitting at the foot of the Nasu Ropeway, it has long served as a base for hikers exploring the Nasu mountain range.

The main water is a colorless, transparent and gentle simple thermal spring, while a separate source of simple sulfur spring feeds the private indoor bath, so guests can enjoy two waters of contrasting character. The inn draws on several of its own sources with temperatures ranging widely from 39 to 72 degrees Celsius and is celebrated for its abundant flow. Its signature feature is Kawa-no-yu, a vast open-air bath created by damming the very river of hot spring water that runs down the mountainside, a rustic mixed-gender bath spread over roughly 100 meters of flowing water.

The baths center on Kawa-no-yu, a collective name for five open-air pools that run downstream as Momiji, Shirakaba, Ajisai, Azami and Yamayuri, supplemented by gender-separated indoor baths, a women-only open-air bath, a family bath and a drinking-water spring. In the mixed-gender Kawa-no-yu, bathers wear a bath towel or bathing garment as they have since the inn's founding, and the uppermost Yamayuri-no-yu is reserved for women. Day-trip bathing is also available, letting visitors sample this hidden-spring atmosphere for 1,300 yen per adult.