This is a very fun and interactive project. It is great as a present or toy. Everything was printed and tested. Version 1 is easy as you can see the maze, but 2 and 3 are inverted so it is harder to solve. The key is hollow to put messages or small presents. (20mm diameter) Cool way to give messages to friends if you want them to have a tough time opening and reading. All 3 designs have the same maze structure. Only the outside is different.
rep-rap universe PLA
This was printed on a modified tarantula not a stock one (cooling fans required)
It takes about 45 minutes to an hour for each part (depending on version and print settings).
This is not a new invention many people made things like this, but it is completely developed and designed from scratch as you can see from the different versions. I used Fusion 360 for CAD and slic3r Prusa edition 2017 version for printing. The design has 0.35mm clearance.