I'd like to have a go with the Superplexus 3D maze toy, but it seems out of stock everywhere. Dang.
I stumbled across the Superplexus while I was looking for a toy I played with as a kid. It was a cube about 3½" on a side, and the inside was divided into about 6 layers, each of which was a maze. Everything was made of clear plastic and the object was to maneuver a tiny steel ball bearing from in-hole to out-hole. Looks like I'm not the only person looking for one.
And no, I don't mean the Money Maze. That looks too simple.
It might have been the "A-Maze-Ing" toy, but I remember each level being more complex than the one in the linked image.
It's from that (possibly false) memory that makes me think it would be fun to craft a complex many-layered blind maze cube, possibly out of wood. My idea is that there would be a gate near the in-hole which would prevent the ball from coming back out; the only way to solve the puzzle would be to work it through to the out-hole.