In the late 1800s, the good folk of Hakone, Japan (in particular three men named Okawa, Okiyama, and Kikukawa) expanded on an idea and invented something called a Puzzle Box (karakuri bako) or Secret Box (himitsu bako). I had heard of them before but didn't know exactly what they did.
Then just the other day my son received one from his grandparents as a souvenir (this and the black eggs). It is pure awesome.
Here's a picture of what his Puzzle Box looks like. It's gorgeous inlaid wood. Or better yet, this. It's a technique called yosegi.
Here's a close up.
I mean that alone is amazing. But that isn't what makes it 'secret'.
What makes it secret is that you can't just open it. It's impossible. You have to slide the pieced together slats of wood in a certain order and a in a certain direction, before it will open. The order has to be exact. J's box is one that opens in 14 moves. But they make boxes that open anywhere from four moves to over a hundred moves.
To close it you have to slide them in the opposite order or it won't shut.
Here it is after a couple moves.
They say that the art of making these boxes has never been written down and has been instead passed down from generation to generation. One of those links up there say there are only nine craftsmen alive who can actually make one and only three apprentices learning the craft. I'm not sure I believe that. But I do believe the not written down part.