Hole in the Door
Editor's Note: If you want to do this trick on a hollow-core door, you have to stick close to the outside edges. Look at the door from the top and you'll see how wide the solid internal frame is.
Hide a Key In Plain Sight
Say you want to hide a key—other than under the rug or over the door. How about mounting a phony plastic LB fitting? Screw it to the wall and run a bit of 1/2-in. conduit to the ground so it looks official. Cut the head off the bottom screw and glue it in place. That's it. Swing the cover aside and there's the key.