So I just posted this on steam as well because I thought it was interesting. In the arsenal right as you enter the room and turn left, one of the monster holes is there, if you run inro it you can glitch through the wall. It doesn't lead anywhere and you can only move in a tiny square inside the wall. I happened to find out because I just absent mindedly decided to run at that hole for some reason,

Pointless? yes... but I though it was still interesting to share anyway.