A secluded hot spring inn located in the deep mountains of Nasu Yumoto in the northwestern part of Nasu Town, Tochigi Prefecture, at an altitude of approximately 1,100m. This historic hot spring inn was established during the Ansei period of the Edo era (1854) and is also known as "Tengu Onsen" (Tengu Hot Spring), with tengu masks displayed throughout the facility.<br><br>Built quietly deep in the Yosasa River valley, the wooden buildings from three different eras - Edo, Meiji, and Showa - blend together to create a retro atmosphere. Famous as a filming location for the movie "Thermae Romae," it is known as one of Japan's most renowned hidden hot springs.

The inn features five different baths (Tengu-no-yu, Ai-no-yu, Kawara-no-yu, Me-no-yu, and Oyogi-yu). The particularly notable "Oyogi-yu" (swimming bath) is a giant hot spring pool that allows mixed bathing (swimwear permitted), offering an open-air experience like a natural pool. With abundant free-flowing hot spring water and accessed via a 10-minute walk along a valley path from the parking area, it truly deserves its reputation as a hidden gem.