Cylindrical Puzzle Box
You see the box here in cherry, although I also have a slightly larger prototype in basswood. The basic idea is that you must work the latch through the maze by twisting the halves of the box around as you pull it open. The latch is sprung so it's not necessary to go through the maze again to close the box -- you can just squeeze it shut. Pretty straight-forward, right? But there's a twist: the maze has no simple solution... the path is just dead ends. In order to solve it, you need to feel around for the parts that you can't get to, and then carefully close the box a bit. This lets you pop the latch over a wall and into a different section of the maze. Repeat and you can eventually get it open.
I had the idea for this puzzle box awhile ago, but it took me over a year to finally complete it. This included making an extra-long boring tool and an aborted attempt at cutting the box halves on my small metal lathe. Eventually, I happened to be visiting my dad and found that his large wood lathe was the right tool for the job. The maze tracks were cut with a rotary table on my milling machine, and squared up by hand with a chisel.