Quanon

Yeah, at the entrance of your cylinder room. Where it the hallway connects.

If look at your second render picture, you see that the render engine kind of makes a mistake there. A sharp triangle looking shadow.

At that spot, both left and right, you have some floating vertices. I would connect those.

EDIT: In editable poly; go to select by edge, then scroll down in the options, find the button CREATE.

With that you can make new edges between Vertices.

Just click from one vert to the other.