Cozy Sauna Lab

A fully private sauna booked by the hour, for one to four people. There are two tubs next to the sauna, and either can be set up as a warm bath or a cold plunge, so you can pair warm with cold or go cold with cold. Cooling off happens in an open-air space attached to the room. Reviewers mention that you can choose the sauna temperature yourself, which suits first-timers, and that sauna wear and a gown are lent out so you can arrive empty-handed. It is a sauna only, with no onsen water. Under-18s need a guardian with them, and the sauna is not open to elementary-school children or younger.