Inside Walls Of Building Model Are Invisible

For some reason if I’m inside of my building model, it’s like the walls don’t exist (like I’m not even in it). From the outside, they are there. Is this a normals issue? I remember seeing something about this, but I can’t remember what the issue is. I know it’s a really quick fix.

Thanks!

Polygons are one sided unless otherwise specified. For walls you should give them thickness and have a surface for the other side. That is, if you want the other side visible.

Thanks a ton, Darth.