This project from Donaldson Workshop is a custom drawer box with a secret compartment in the center. The drawers all have stops so they cannot be removed. An object can be entered behind the drawers and rolled through a maze to reach the felt lined secret compartment...
Makezine recently featured this video on how to build a multi-book secret storage box. Starting with a group or series of books you can conceal a much larger compartment. You can also use a jig or a scroll saw to avoid the tedious process of cutting individual pages...
This custom built-in bench includes additional storage in the corner. The L-shaped bench is fitted inside a tiny home and has a trap door that opens in the corner to reveal the hidden storage compartment.
This portable Döttling jewelry box secures into a larger luxury safe. It docks inside the safe to charge a GPS unit. When removed from the safe it can be tracked anywhere in the world.
A new home owner was surprised to find a room in his basement with a lockable steel door. He found only an empty safe inside, and thought nothing of it. When he went to work on the pipes, though, he found a stash of silver worth around $2200. This page has more pics...
