In the very beginning of the game, right when SCP 173 attacks the guard at the top, if you walk backwards into the wall on the opposite side of that big room (not the containment chamber), you can glitch through the wall into nothing. i was still on the same "floor" for a while, but soon i dropped below and was still in some kind of void where i could see into all these rooms but could not glitch back. this happened on my first playthrough so idk whats going on XD