Hiratanai Onsen Kuma-no-Yu is a free wild outdoor hot spring (noyu) located along the Hiratanai River in Kumaishi Taira-cho, Yakumo Town, Futami District, Hokkaido. Situated approximately 3 km upstream from Kumaishi Hiratanai-so inn at an elevation of about 250 meters, this rustic hot spring was developed following new drilling in 1972. The natural open-air bath is carved into rocks beside the clear stream of the Hiratanai River, creating an incredibly open and scenic environment. It is famous among wild hot spring enthusiasts and gained national recognition after being featured on the popular Hokkaido TV show 'Suiyo Dodesho' (Wednesday How Do You Like It?) during the 'Battle Against Hemorrhoids' episode.

The source water temperature is approximately 70°C, so bathers must adjust the temperature themselves by pumping cold river water through hoses. The spring quality is sodium chloride (pH 7.4, neutral) with a slightly tea-colored appearance and a characteristic salty taste with a faint iron-like aroma. The therapeutic benefits include treatment for rheumatic diseases, neuralgia, lower back pain, motor dysfunction, hypertension, and digestive disorders. This is a mixed-bathing wild hot spring with separate simple changing rooms for men and women.

The hot spring is free and available 24 hours, but only operates from late April to the end of October, closing during winter. From the spacious parking area, it is about a 5-minute walk along a paved path. Popular among campers and motorcycle touring enthusiasts, it offers a wild and authentic hot spring experience in nature. Visitors should be cautious of bears and biting insects (black flies). As the facility may be temporarily closed, it is recommended to check the latest operating status before visiting.