I messed up. I wanted to switch out the bottom bracket on my bike. When I tried to do that the toothed cup on the left side (non-chain side) sheared off. The entire thing is now plain with its housing.
edit says: The other side is also not removable as the teeth got - for lack of a better word - destroyed when I tried to unscrew it. Didn't even apply that much force.
Is there a way to remove it without damaging the frame of the bike?
For reference: The 'destroyed' toothed cup you can see in this picture is what I'm talking about. In my case the cup is made out of plastic (I guess, based upon the fact that before it tore off some teeth got shredded).
The other side - the one with the sheared off bit - was more stubborn and in the end a heat gun, a screw driver and a hammer were necessary to get it out. It was done by heating the cup up without damaging the frame or the bowden cable guard and then hammering the screwdriver into the inside of the cup in a way that unscrewed the cup. The thread of the frame into which the cup was screwed got damaged slightly.
Since Nathan's answer got the first cup out, I'm going to mark his as my answer.