Kawaura Onsen

Kawaura Onsen—River Inlet Spring—is a saline thermal spring in landlocked Yamanashi Prefecture, its sodium chloride mineral character speaking to the ancient marine geological formations buried beneath the Kofu Basin where the minerals of vanished Mesozoic seas persist in the volcanic substrate that now produces thermal spring water of unexpected saline character. Saline springs are valued in Japanese balneology for their exceptional heat-retaining properties—the yudamari quality of salt springs, which warm the body deeply and maintain elevated core temperature long after the bath has ended—making this Yamanashi saline spring particularly beneficial in the cold mountain winters of a highland prefecture surrounded by Japan's highest peaks. The river inlet name, suggesting a spring found where a watercourse meets a broader body of water, connects this inland saline spring to the ancient marine geography that explains its improbable coastal mineral character deep in the Japanese Alps.