Across Japan, different kinds of public bathing facilities range from onsen (natural hot spring water) to sento (public baths) with added features such as rotenburo (open-air baths) or saunas.

The 260-square-meter Hiba Sennin Buro (1,000-person cypress bath) at Sukayu Onsen, which lies at the western foot of the Hakkoda mountain range, maintains separate timeslots for mixed bathing and ...