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Fuji-Hakone-Izu NP, Tokyo
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The sea acts as Jinata’s thermostat: spring water can exceed 80°C at low tide, but incoming seawater cools the rocky pools. As the tide shifts, bathers move between pools to find a comfortable temperature.
Jinata helps researchers study ancient iron-rich oceans: a 2019 study found likely iron- and hydrogen-using microbes near the spring source, then abundant, active cyanobacteria downstream—even with about 150 μM iron.
Islanders call moonlit bathing here “yoshio” (夜潮), or “night tide.” People soak, chat over the surf and wind, and move between pools as the tide changes—making the spring’s shifting temperature part of the evening ritual.
During the Edo period, Shikinejima had no permanent residents, yet people from neighboring islands reportedly came to Jinata for therapeutic bathing with permission. The spring was a destination before the island became a settled community.
Before the path, Jinata could be reached only from the sea. Three stonemasons from Shizuoka, visiting for port work, cut a route through the cliffs; islanders commemorated their effort with an inscription still preserved there.
Old cliff faces bear names and thanks left by former bathers; some visitors even brought iron chisels to mark their visit. Those weathered inscriptions remain, but carving or damaging the rocks is prohibited today.
In 1919, haiku poet Hagiwara Seisensui visited Jinata and wrote of a sick person embracing a rock warmed by the spring. It’s a vivid image of how closely the bath and the island’s raw volcanic rock meet.
On the approach, a square opening called the Yukagen-no-ana, or “temperature-check hole,” vents warmth from a volcanic crack about 400 m north of the spring. It’s a charming local curiosity, though not a dependable thermometer for the pools.
Jinata takes its name from a landscape that looks as if a hatchet cleaved the earth: the spring lies down a steep, narrow cleft between towering rock walls.
In a 1981 outdoor-bath ranking selected by travel writer and hot-spring critic Fuyuto Noguchi, Jinata earned the East’s “extra Yokozuna” spot—a sumo-style accolade for a famously rugged seaside bath.
