Hiruzen Yatsuka Hot Spring Kaiyukan

Kaiyukan in the Hiruzen highlands combines sports facilities with radon-rich hot spring baths in a setting surrounded by mountains. The complex includes tennis courts, a driving range, a soccer field, basketball courts, a pool, and rental bikes, plus a ground golf course, a Japanese adaptation of the sport using a wooden mallet and played over short distances, suited to all ages. The hot springs here have some of Japan's highest natural radon concentrations, produced by uranium decay in the igneous bedrock. Indoor facilities include stone baths and saunas; the outdoor baths overlook small gardens, with clear night skies making stargazing a regular draw after dark.