The objective is simple : find the smiley face
...but where to start? Well, that's part of the puzzle! This puzzle box prints in one piece (except for the key) so you can try to solve it straight off the print bed.
My only rule for solving is no sticking your fingers inside the puzzle (otherwise it's possible to cheat!)
Print the "MysteryPuzzle" and "MysteryPuzzle_KEY" STL files for the print in place version.
If you don't mind ruining the surprise (aka printing for someone else) you can print the "_pinOnly" and "withoutPin" STL files in place of the combined "MysteryPuzzle" model. This may be easier to print, plus you can make the pin stronger (4 shells) and the body itself can have 2 shells and very light infill.
Print at .15mm layer height or parts may not work correctly! This design does demand a properly tuned printer.
This prints great on my Ender 3. If you have any problems share in the comments. I want to make my files as universally printable as possible!
*I have edited the puzzle slightly since photographing, so some things may look slightly different*
Pictured in MatterHackers PRO PLA -- blue and yellow...clearly :P