Via Apartment Therapy (and circulated pretty widely around those interwebs at this point), this staircase was modded to perfection. I love that it automatically keeps all of the books looking neat and tidy.
I have always been a fan of the idea of hidden rooms and secret passageways. But when you think about a bookcase for a door, it really does help free up some space and add a bit of intrigue.
Via Neatorama (who found it over at WebUrbanist), Creative Home Engineering crafts custom hidden doors that can look like kitchen cabinets, bookcases, stairs and even working dressers.