Loaded with major ions — the essential minerals (Ca, Mg).
Buoyancy
Effortless float
LowHigh
Dense, salty water — you float without effort.
SodiumChloruresBrome
Yakushima Island, a UNESCO World Natural Heritage Site off the southern tip of Kyushu, shelters ancient cedar forests where some trees are over seven thousand years old, including the legendary Jomon Sugi ancient cedar. Yakushima Onsen Hirauchi Kaichu is a remarkable tidal hot spring, submerged beneath the sea at high tide and accessible only two hours before and after low tide, offering an otherworldly open-air bathing experience on a wild coastline. Chloride-rich thermal waters mingle with the Pacific salt air, creating a primal and unforgettable onsen ritual in one of Japan's most extraordinary natural landscapes.
Insider tip — Hirauchi Kaichu Onsen on UNESCO-listed Yakushima island is a tidal pool bath on the rocky Pacific shoreline that is submerged entirely at high tide — the precise window for soaking is only a few hours around low tide each day. The sodium-chloride water blends with Pacific surf in a surreal natural infinity bath surrounded by ancient cedar forest above. Check the daily tide tables carefully and bring a towel in a waterproof bag for the coastal walk.
