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Kirishima Kinkowan NP, Kagoshima
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A 1546 report gives Ibusuki’s oldest known sand-bath account: villagers on the Yamagawa coast dug just 22 cm into the beach at low tide, then lay in warm sand for 2 hours as the water returned.
The beach heats itself from below: inland geothermal pressure heats groundwater above 90°C, then cooler, denser seawater helps push it up through the shore sand. Nature supplies Ibusuki’s under-sand heating system.
Ibusuki’s volcanic bath sand is a black-and-white mix, coarser than ordinary beach sand and flecked with iron sand. The larger grains leave tiny air passages beneath the warm covering sand.
About 4 km southwest, at Lake Unagi, volcanic steam does kitchen duty: cooking devices called sume use fumaroles to steam potatoes, eggs, chicken and more. It’s a separate neighborhood tradition, powered by the same underground heat.
At Saraku, a favorable low tide and good weather can move the sand bath from its covered coastal facility to the water’s edge. High tide or poor weather means bathing under the roof instead.
In the early Edo period, Satsuma lord Shimazu Mitsuhisa built a hot-spring retreat at Surigahama and named the spring 神井 (“divine well”). An 1843 domain gazetteer credited its sand bath with easing illness and muscle pain.
Though it reaches the beach beside the sea, Saraku’s spring water has about 7,000 mg/L of chloride ions, compared with seawater’s 19,000 mg/L. The bath’s operator says ancient fossil seawater is the leading source theory.
On Ibusuki Port beach, researchers found natural sand-bath conditions when sand 20 cm down measured 65–80°C and groundwater lay just 30–60 cm below the surface; the sand cooled as the water table deepened.
At Saraku, the specialists who cover bathers are called 砂掛師 (sand-coverers). In 2025, Ibusuki held its first city workshop to pass on their skills, including checking sand temperature and shaping a level bed.
In a 2026 study, 14 healthy young men tried 20-minute steam-sand, hot-water and sauna sessions. Sand bathing felt most comfortable and raised core temperature least; post-session blood-pressure drops were similar.
