Build a Secret Spy Bookcase
Building a secret spy bookcase is not as difficult as it may sound. Who wouldn't want a secret lair all to themselves? Learn how to make your own.
Instructables member nylanan provides simple plans for a hidden door. Check it out:
Another example from flickr member agmk (unfortunately no instructions posted). Hack N Mod explains, "This door is dirt simple to create. It's literally just a bookcase put on standard door hinges with coasters added to the bottom. "