Introduction
Kawayu Onsen is a hot spring hamlet on the Oto River, a tributary of the Kumano-gawa, in Hongu-cho, Tanabe City, Wakayama Prefecture. Its distinctive feature is that hot water bubbles up directly from the riverbed, letting visitors dig their own riverside pools where scalding spring water mixes with the river's cool current. In winter (December–February) the riverbed is turned into Sennin-buro, one of Japan's largest open-air baths, accommodating around 1,000 bathers, and the area is a convenient base near the Kumano Kodo trails and Kumano Hongu Taisha shrine.