This secret door on Hometalk is a good example of a faux bookcase door. It looks like a bookcase from a distance, but to safe weight and space the bookcase have been cut down and permanently affixed to the shallow shelves. While not making the space useful as both a door and storage space, this method does still conceal the door to casual observers. A thin bookcase door like also allows more side-to-side clearance through the passage than a real bookcase would allow when it’s open.