Hirauchi Kaichu Onsen

Hirauchi Kaichu Onsen sits on a rocky beach on Yakushima's southern coast, accessible only during the two hours before and after low tide, twice each day. A timetable posted nearby shows the day's access windows. The three outdoor pools, each holding about 15 people, were built from piled rocks, with a local tradition tracing the discovery to steam rising from the beach around 400 years ago. Water temperature runs between 38 and 40 degrees Celsius, varying slightly with the tides. All baths are mixed-gender and free to enter, though a 200-yen donation is requested for upkeep. The combination of warm water, sea view, and tidal timing makes this one of the more memorable baths in Japan.