It’s a regular gym that also has a sauna. Around 40€ per month will get you a gym with sauna in most cities in Germany I would say.
In London, I can't find a gym/pool combo that is under 120gbp a month, and even at this minimum price; they're 1.2 meters deep and filled with sand, band-aids...and I am not kidding I saw a menstrual cup in one of them once.
I haven't been swimming since then.
I don't get London.