Located in the valley along the Shimura River (a tributary of the Kumano River) in Wataze, Hongumachi, Tanabe City, Wakayama Prefecture, Watarase Onsen is nationally famous for having the largest open-air bath in western Japan. Although it is a relatively new hot spring area that opened around 1963, together with Yunomine Onsen and Kawayu Onsen, it forms the Kumano Hongu Onsen Village, which was designated as a National Health Resort Hot Spring in 1957. The large open-air bath is divided into 5 pools, each set at a different temperature, with an overwhelming scale that can accommodate approximately 500 bathers at once. The water quality is a sodium bicarbonate-chloride spring (neutral hypotonic high-temperature spring), with the source name Tensho-no-Yu, pH 6.7, source temperature of 60 degrees Celsius, and a flow rate of 199 liters per minute. Known as Bijin no Yu (Beauty Water), this natural sodium bicarbonate spring flows directly from the source (kakenagashi), and is highly valued for its skin-beautifying effects that leave skin silky smooth. The facility includes two accommodation options, Hotel Sasayuri and Hotel Yamayuri, and features 8 private baths (4 family-exclusive and 4 rental baths) in addition to the large open-air bath. Located just 10 minutes by car from Kumano Hongu Taisha, it is a popular resort base for Kumano Kodo walking, with beautiful seasonal scenery and stunning starry skies at night.