Kaniyu is a secluded hot spring inn located at an altitude of 1,350 meters in the deep valley of the Oku-Kinugawa Onsen area in Nikko City, Tochigi Prefecture. Situated in the headwaters of the Oku-Kinugawa region, known as the last unexplored region of Kanto, it lies within a nature conservation area inaccessible to regular vehicles. The inn is approximately 25 minutes by shuttle bus or 1 hour and 30 minutes on foot from Meotobuchi, truly befitting the term "hidden hot spring."

The history of Kaniyu dates back to the Edo period when the Komatsu family used the location as a hunting base. After being buried by landslides from a typhoon in 1902 (Meiji 35), it was rediscovered in 1927 (Showa 2) by Komatsu Minekichi, the great-great-grandfather of the current owner. After serving as an unmanned hut during the pre-war and post-war periods, it opened as a hot spring inn in 1934 (Showa 9). Originally called Kaniyu (crab hot spring) due to the abundance of freshwater crabs, it was renamed to the current Kaniyu with different characters in 1950 (Showa 25). Its roots as a mountain hut are still evident in its rustic atmosphere.

The inn's greatest feature is its five private hot spring sources with different water qualities: Kogane-no-yu, Oku-Kinugawa No.4, Iwa-no-yu, Gake-no-yu, and Take-no-yu. Each source has different temperatures and components, embodying the concept of "Ichigo Ichiyu" (one encounter, one bath) promoted by the Tochigi Cloudy Hot Spring Association. While the source water is colorless and transparent, it transforms into milky white or bluish-white when collected in baths, depending on temperature, atmospheric pressure, and water volume, showing different expressions daily. Known as a beauty bath, it is reputed to make skin silky smooth.

The outdoor baths are scattered along the Kinugawa River headwater valley. The First Outdoor Bath is exclusively for women, while the Second and Third Outdoor Baths are mixed bathing but allow single-colored bath towels. The Third Outdoor Bath is particularly famous, offering views of the columnar jointed rock face and Byobu Rock across the river. At "Kikuyu Roman-no-yu," visitors can compare all five sources individually, offering a rare experience nationwide. At 1,350 meters altitude, temperatures rarely exceed 30°C even in summer, providing natural coolness without air conditioning. Open year-round, winter bathing with snow-covered scenery is especially popular.