For everyone who wanted a secret passageway or closet when they were kids, these are for you: Woodfold Custom Bookcase Doors.
The Oregon company's Bookcase Door System is an intriguing storage solution for small spaces -- or secretive people. With fixed shelves at the center and bottom, and four adjustable shelves, the bookcases will support up to 500 pounds. (Although we're not sure how you stop the books and objets d'art from flying unless there's a lip at the edge of each shelf.)
Woodfold's other products include roll-up doors, accordion doors, and hardwood shutters.
Since they're custom-built, the price varies.