Schwuz (bar/club) is not at Meringdamm (Kreuzberg) anymore, it's been at least a couple of years since they moved to a new location in Neukoln. Never been to the new location.

Saunas, just as perthflyer said.

Der Boiler in Kreuzberg has much nicer facilities.
Apollo is older and hasn't been renovated for a while (at least, last time I was there).

Der Boiler attracts a more younger crowd (younger than 40s)
Apollo is more diverse.

I think Apollo crowd is more down to earth and more willing to engage.
Not that you can't engage at Der boiler on a Sunday afternoon, it is very happening as well.

Enjoy!