I am member of Jetts, a fitness chain with 24/7 access to clubs. My Jetts in Eindhoven is only partially staffed. It means: sometimes two or three men working out in an empty club. What more do you need for sexual adventures?
But... reality is that we all are anonymous, doing our own routines. Yes, a face of recognition here, a greeting there. But mostly we all do out own routine. The one on the tredmill, the other with the weighlifts, the other on a rowing machine. There is not really interaction between the visitors. Not at my club.
There is also no habit of using the showers. Most visitors shower at home. So it is hard to imagine any sexual encounter in my club. But maybe other clubs have a different culture. No idea. I only chose this one because it is closest to my place.
Of course I have fantasies about hotties in the club, but that is what it is: fantasies.