I cool little model train that has a secret compartment inside. You unlock it by pulling the whistle up, then can remove the compartment by pulling on the handle that looks like a coupler on the back of the compartment.
The compartment is big enough to hold money, cards, keys, or other small valuables. It can be a great looking model to leave on a shelf and hide things in plain sight.
Things to NOTE:
All of the parts are designed where you can orient them to print without supports EXCEPT the train whistle.
For a complete model you need to print one of everything, but multiple wheels. I put 6 wheels on my own model, but you can put as many as you like.
The file "train parts" contains 6 wheels, the smoke stack, and the light. This way you have one file with all of the parts together that you can throw into a slicer if you wish.
The model comes together easily with a little bit of adhesive. I used "Liquid nails" which is overkill, but it is all I had. I painted mine for a nice finish, this is not required, but will keep people from seeing inside it if they hold it up to a light. Both the whistle and the smoke stack have spots in the shell for them to fit into.
The Whistle acts as the lock, it slides through the square hole in the shell and fits into the compartment locking it in place.
I did include some tolerance in the model, but tolerances vary between printers and filaments, so you may have to do a little sanding to get the parts to slide together properly.