Kawayu Onsen

At Kawayu Onsen hot water rises straight through the pebbly bed of the Ōtō River, so with a small spade and a swimsuit you can dig a hollow at the water's edge and mix river water to your preferred temperature for a genuinely wild open-air soak. From December to late February, when the river runs low, the town dams a broad section of the riverbed to create the Sennin-buro, a vast communal bath said to hold a thousand people, open free of charge and lit at night. Because it is a river, bathing requires a swimsuit, and soap and shampoo are not allowed. The spring lies a short distance from Yunomine and Kumano Hongu, and riverside inns line the bank.