Kojin-no-Yu is a communal outdoor hot spring bath located on the riverbank of the Gamata River in Tochio Onsen, Okuhida Onsen-go, Takayama City, Gifu Prefecture. Okuhida Onsen-go consists of five hot spring areas: Hirayu, Fukuchi, Shin-Hirayu, Tochio, and Shin-Hodaka, boasting an abundant flow rate of over 44,000 liters per minute, ranking third after Beppu and Yufuin hot springs. Tochio Onsen was designated as a National Health Hot Spring Resort on November 19, 1968, and was named after the many Japanese horse chestnut trees (tochi-no-ki) that once grew in abundance in this area.

Kojin-no-Yu is an unmanned facility with separate changing rooms and outdoor baths for men and women, with no indoor baths or shower facilities. From the rustic bathing pools surrounded by large rocks, visitors can enjoy views of the majestic mountains of Okuhida, including the Northern Alps, and the clear stream of the Gamata River, offering an exhilarating bathing experience full of natural charm. It is also popular for enjoying the starry night sky, providing a luxurious time to become one with nature. The water is a colorless, transparent simple hot spring, and occasionally you can see fluffy white yuno-hana (mineral deposits) dancing in the water.

The surrounding area attracts many tourists who enjoy mountain climbing and camping, and as a homely hot spring area dotted with unpretentious, rustic inns, it has long been beloved by climbers and anglers. As a conscientious hot spring where you can bathe for a voluntary donation, it is cherished by locals and hot spring enthusiasts alike.