Another trick, in your preview window, right-click for the contextual menu and select the top camera.  Move it up in the Y direction until you see enough of the scene that would include the render camera.  On the Properties/Parameter panel switch to the render camera and you should see its outline in the preview.  Use the directional dials to move that camera inside the room.  If you also use RedPhantom's suggestion to unhide the backfacing polys you should be okay.