Peninsula Hot Springs

The PHS features a hot natural mineral water but with a lot of help.  I have bathed in hot pools in NZ where the water is just running out of the ground and not a cent to pay. Here we have to bore down and bring it to the surface. Nevertheless it is unique in Australia. There are your various spa towns like Hepburn but that one and also Clifton Springs (mentioned elsewhere in ROBOT) started out by getting you to drink the stuff. Later they started heating it for bathing. The closest I have found to this phenomenon is in the NT in Litchfield where warm water cascades into pools after being heated by the rocks it passes over.
I would recommend trying this. Get there on a midweek day not in school holidays, at 9:30am. This allows half an hour for the "No kids on the hilltop" rule to take effect at 10:00am. Don't be put off by the endless cars parked seemingly forever. There seems to be plenty of room to spread out in side.

They do mean Hot

Orakei Korako