This is something I've been working on for a while in between other projects. Only a specific sequence of steps will allow access to its secret compartment. Check out the YouTube video linked below to see it in action.
Designed in Sketchup and printed on my UM3, it's made up of 36 individual pieces which snap together.
I used a variety of filaments:
Ultimaker Nylon, Transparent and Black
Ultimaker ABS, Orange, Green and Gray
Faberdashery PLA, True Lagoon and Glacier Blue
YouTube Video, Project X