Hiruzen Yatsuka Onsen Kaiyukan

Hiruzen Yatsuka Onsen Kaiyukan is a day-use bathhouse at Hiruzen Kogen Sports Park, up in the Hiruzen highlands of Okayama. The spring is a radon water, and there's a cold-water bath drawn straight from it alongside the regular baths. Bathing options include an indoor bath with a glass wall looking onto the garden, a jet bath, a sauna, and two outdoor rotenburo, one set in a Japanese garden and one in a Western one, that swap between the men's and women's sides every week. Inside there's a restaurant and a few different rest spaces, including a tatami room and a kids' corner with toys, so it works as a place to soak and linger rather than just pass through.