Interior Mapping! Maybe awesome?
I saw this over at devbump and it looks like it could be really awesome. It's a texture mapping technique to make it appear that there are interiors to your buildings, even if the building has no interior polys. So instead of seeing an oddly opaque window, you'll see into the building. Screenshots, and tutorial stuff is at the link. Anyone want to give it a shot:
http://interiormapping.oogst3d.net/
Tags: art, environment, interior mapping, model, texture