The traditional sauna runs hot, ninety to ninety-five degrees, the kind of heat that empties your head in minutes. Onsen brought the Japanese bathing ritual to Henley Beach Road in Torrensville and built the whole experience around contrast. You move from the sauna to a warm mineral bath, then into a cold mineral plunge, and repeat until your nervous system gives up the fight. There is a private infrared room and compression therapy for legs that have earned it. Twenty-five minutes a station, no rushing. Adelaide has plenty of saunas now. This one asks you to slow down and mean it.