Glue the spines from an old encyclopedia set to slats of wood, back with a piece of fabric (a "tambour") and top with woodscrews as makeshift rollers that run along a routed track, and voila, you've got a hidden stashbox that slides aside to reveal whatever you want to hide there.
My problem is that if I made this, it would remain a secret for precisely zero seconds as I excitedly showed it off to everyone who would come see it, because it is just that cool.
The original project is by Keith Decent, with a great accompanying writeup by Hackaday's Tom Nardi.
Decent uses "reclaimed" materials (presumably spines from damaged books), but if you're the kind of ignoramus who likes decorating with wrong-way-round books, you could remove all the spines from your decorative elements and sell them to people making these.
When the spines are removed from the books, they get glued to individual wooden slats. These slats then have holes drilled in the top and bottom, and standard wood screws driven in to act as "rollers". Real rollers would undoubtedly make for smoother action, but you can't beat his method if you're trying to get it done cheaply and quickly.
The slats are then glued onto a piece of fabric, creating what is referred to as a tambour. The fabric backing links all the slats together and makes it so that pushing and pulling one slat will move them all together as one. The book spine tambour is then inserted in the routed channel, and the back panel of the shelf can be installed to lock it all together.
At this point the project is essentially done, but [Keith] does take it the extra mile by sealing all the book spines and doing some finish work on the shelf to make it look more like a real vintage piece of furniture instead of some scrap plywood screwed together.
DIY Bookshelf is More Than Meets The Eye [Tom Nardi/Hackaday]
