Gozinta Box
These two files are the top and bottom of a Gozinta Box, part of a magic trick/illusion invented by Lubor Fiedler. Print two tops and two bottoms to make two boxes (preferably print the two boxes in different colors). You'll discover that box 1 can fit fully inside box 2 (it "gozinta" the other box), and box 2 can fit fully inside box 1. This is accomplished without stretching, bending, forcing, trap doors, or secret swapping of boxes.
This box is a remix of Lichtagent's design. The only difference is that I added a hole in the bottom of the bottom box half. The hole allows air to escape when the top half lowers over the bottom half and gives a way to grasp the bottom—if needed—when pulling the box halves apart.