Hirauchi Kaichu Onsen

Hirauchi Kaichu Onsen is located along the coastline in the southern part of Yakushima, where visitors gather around the time the tide begins to recede. The key feature of this spot is a natural hot spring pool that appears on a rocky shore, normally submerged beneath the sea. At low tide, this rock-enclosed bath emerges, allowing access for roughly two hours around the time of low tide.

The hot spring water flows directly from the seafloor, and the pool is completely underwater during high tide, so bathing is only possible during limited periods each day. The surroundings consist of an unobstructed view of the open sea and rugged rock formations. Visitors can experience the changing sea conditions while listening to the sound of waves crashing nearby. The bathing area uses the natural coastal terrain without any artificial structures.

To use the onsen, it is necessary to check the timing of the low tide in advance, as access depends on the tidal schedule. The changing area is simple, equipped only for undressing. Given that this is a shared natural site, users are expected to observe local rules and be considerate of others. At this rocky coastal setting, people sit quietly in the hot water, accompanied by sea spray and shifting coastal scenery.