I have been a couple of times across a couple of decades. I have found the atmosphere a bit strange compared to other gay saunas in other countries. I have an average size endowment when hard. When soft, it shrinks up into a tiny package, a grower not a shower. What I remember from the place is a lot of guys - presumably mostly Germans - walking around with big d***s dangling looking serious, if not mean. I felt out of place. I've been to gay saunas in London, Amsterdam, Paris, and Vienna and never felt that way.
The first time I went, when I was much younger, I did end up hooking up with someone after wordless play in the hot tub. We went back to his room where I found out he was an American from LA. The second time I went was many year later after an evening at Oktoberfest. The sauna was packed. I might have as well as have been invisible. I felt out of place, even unwelcome. Maybe if you have an above average endowment, they'll make you feel more welcome.