Gaga Onsen

Gaga Onsen is a single, secluded inn deep in the Zao mountains, part of a nationwide association that protects Japan's hidden hot-spring inns. The water is clear and runs 100% kakenagashi, straight from the spring. You can bathe several ways here: a hot atsu-yu (あつ湯) bath taken in the inn's traditional kakeyu (かけ湯) style, a milder nuru-yu (ぬる湯) you can soak in for a long stretch, and an open-air rotenburo set right in Zao's forest. Further past it is a mixed-gender bath by the river, reportedly closed in winter when avalanche risk runs high. There's also an unreserved private outdoor bath called Tenku no Yu (天空の湯), open into the evening and again from sunrise the next morning, plus a ganbanyoku heated-stone room and one guest room, Komakusa, with its own in-room hot-spring tub. The spring dates back some 150 years to the early Meiji era and has long been known as one of Japan's three noted springs for stomach ailments (Nihon Sandai Ichobyo no Meito, 日本三大胃腸病の名湯); guests still drink the water here as part of that old cure tradition. There's no cell signal in the rooms or halls (Wi-Fi only in the lounge), no other inns or restaurants nearby, and the place is reached mainly by car or a once-daily shuttle.