I did two versions of a puzzle box, or Jacob's Ladder. The one on the right (blue) is the more usual version. The black box on the left is actually made up of two trays...though I know it's difficult to see because of the monochromatic colors.
I came into the studio this morning with an idea in my head...something about trying to create a hidden page on the top of a box and using a magnet to be sure that the page stayed closed. I created a model out of mat board to see where problems might exist and then did a full box with a hidden "page" on top of the lid. A tiny magnet is embedded under the bird illustration so it snaps closed. So far, no one who has handled the box without knowing about the page has found it. The question we're talking about in the studio is whether to provide a clue on the box, or simply let it be.
The final box here has been our most challenging. It's 3 trays on a wrap case which wind up and close tight with a magnet. As each tray unrolls, it's covered by the top of another tray. I think each of us has had success in the end with the box, but there have been many stressful moments along the way.