Chi 鉈 Onsen

A wild tidal onsen on the rocky shore of Shikine Island, reached by descending 193 steep steps into a V-shaped sea cleft. The spring itself hits 80 degrees at the source, but as the tide comes in, cooler seawater mixes in, the sweet spot for bathing is the 90-minute window around high tide. Pick your pool among the rocks and share it with the occasional crab. Swimwear is required, and the experience is as raw as outdoor bathing gets.