Yachi Onsen is one of Japan's three great secret hot springs, with over 400 years of history, nestled in the mountains at an elevation of 800 meters on the slopes of Mount Hakkoda. The other two secret hot springs are Iya Valley Onsen in Tokushima Prefecture and Niseko Onsen in Hokkaido. This solitary ryokan is embraced by the vast beech primeval forest of Yachi Wetlands, inviting visitors into the ancient hot spring culture. The hot spring water is a direct foot-welling natural spring, where the water gushes directly from the bottom of the bathtub. Both men's and women's baths feature two different types of spring water: Kami-no-Yu (upper bath) is 42°C hot water with simple spring quality (hypotonic weakly acidic low-temperature spring), and Shimo-no-Yu (lower bath) is 38°C warm sacred spring with clear simple sulfur spring hydrogen sulfide type (hypotonic weakly acidic spring). The Shimo-no-Yu is believed to be effective for neuralgia, arthritis, back pain, and atopic dermatitis, with a temperature setting that allows for extended soaking. The inn consists of three buildings: the main building, east wing, and west wing, with a total of 36 rooms offering views of the seasonal mountain scenery through large windows. Despite being a remote secret hot spring, free WiFi is available in some areas of the facility (front desk, lobby, and parts of the restaurant), and although mobile phones are out of service range, comfortable amenities are provided. During the winter season (November 1 to end of April), the inn is closed on Tuesdays, Wednesdays, and Thursdays.