A 5x5 sliding puzzle.When you complete the puzzle on one side, the other side becomes jumbled. So flip it over and continue!
This prints fully assembled, no assembly required. I printed at 0.35mm layer, but I expect any resolution to work.
How your printer is calibrated and the current thickness of your filament will affect the thickness of your print. So I've included 5 different STL's with an increasing gap size. Each STL has a number in it, this is the gap between the pieces in tenths of a mm. So start with 4 and increase or decrease that number if the print is too tight or loose.
4&5 work for my printer so I expect the range provided should cover most. Let me know if you need more.