It's a hole left from doing a projection on the wall of a square. I did have a frame around the window but when I found that my first try at lighting from the outside and doing an image plane outside the window wasn't going to work, I filled in the hole (DO OVER!!! ). Now, I think I want to try it all again, even though the more I add to my scene, the longer it'll take to render. I'm stubborn like that.

- Russell