It was a puzzle in area A, where a ball is moving back & forth along a path inbetween two rows of guns and you have to somehow get a box through it. It's a fun puzzle and it introduces a "new technique", in the order I've done the puzzles at least. Anyway, the puzzle walls have windows and after I solved the puzzle I found that by standing on the box, I could jump though one of the windows (only one, although they all look virtually identical) and "escape" the puzzle. There wasn't much to do outside though from what I could see, apart from running around the outside of the walls. I might have another look incase I missed something.
Incidentally, while wandering around "the outside" I found a glitch where if I stood in a certain spot the nearby wall disappeared. The trouble is, with the nature of the game, I don't know whether it's deliberate or a genuine bug!