Kinkayu

Widely considered the hardest-to-reach wild hot spring in Japan. The route from the forest road gate involves hours of riding or hiking through bear country and stream crossings, with parts of the path completely washed out. The reward is a single pool atop a limestone terrace where the source water emerges colorless but turns milky blue-white in the bath, rich with calcium and a faint sulfur edge. A serious undertaking, not a day trip.