I went to a second, VASTLY superior climbing gym tonight. It's on the U2, not even that far out of town, and in a neighborhood I felt way safer in than Der Kegel.
It's bouldering only, and it's huge! Tons of climbing walls of all heights and angles, and some really interesting problems, including a few "feet-only" ones. It is a bit more expensive than Der Kegel, but to me it's worth it. It's also a lot cleaner, and the staff was way more attentive and helpful. This would be my gym if I lived in Berlin!
I realize these posts would be infinitely more interesting if I had some photos to share...