Hokkawa Onsen Kurone Iwaburo

Kurone Iwaburo is a municipally operated communal open-air bath set right at the water's edge, at sea level, on the Sagami Sea coast of Kitagawa in Higashiizu Town, Shizuoka Prefecture. Hokkawa Onsen is said to date from the early Showa era, when local fishermen noticed hot water welling up offshore and drilled along the shoreline to tap the source. The bath itself has more than sixty years of history, and its head-on view of Izu Oshima island, together with a position so close to the sea that spray reaches the pools, has made it one of Izu's best-known open-air baths among hot spring enthusiasts nationwide.

The water is a sodium-calcium chloride spring, listed under the older classification as a weak saline spring containing gypsum. It carries a faint saltiness befitting its seaside setting and retains heat well. The source emerges at around 70 degrees Celsius, with a pH of roughly 7.9 (weakly alkaline) and a total mineral content of about 3.7 grams per kilogram. The water is delivered straight from the source without heating or recirculation, with an attendant managing temperature and flow. It is clear and colorless, with no chlorine odor, and leaves the skin warm long after bathing.

Three rock pools face the sea: the two nearer pools serve men and the round pool at the far end serves women, in fully separated bathing with a dedicated women's passage. The bath was once mixed-gender but was separated under administrative guidance. There is no washing area or shower, and changing space is minimal. Admission is 700 yen for adults (revised in January 2025; free for guests staying at Hokkawa Onsen inns), and hours are 10:00 to 18:00 with last entry at 17:45. The bath closes in stormy weather. A free parking lot holds about ten cars.