Cube with Hole
This is an interesting little mathematical anomaly, my boss told me it was possible to cut a hole through a cube large enough to pass a cube with the same size through it. He did all math by hand, rotating the cube to optimum position and then drawing the net for the cube. It almost felt like cheating when I came home and knocked it up in a CAD package.
I unwrapped it for assembly from card stock, but I'm also supplying the stl files because I think it would be great if it were 3D printed (If anyone does that, please post photos). (pdf here)