I've uploaded "Box Short.stl" and "Lid Short.stl" which are 62.5% of the original height of the box for those not requiring the size of the original box. These components also include a minor improvement in the design of the hidden corners for assisting in holding the box closed. I test printed both components and they printed fine.
END OF UPDATE.
I've seen many of these over the years, the latest I found a few years ago made of wood. This 3D printed version is a very simple, yet pretty effective "secret" box.
Even with pretty close examination, it appears as if there is no way to open the box. Only by gripping the correct opposite corners on the correct end and pulling, will the box open.
Designed using Sketchup Make 2015, and printed in PLA on a Makerbot Replicator 2 using Makerware 184.108.40.206 "Standard" Settings (.2mm layer height, 2 shells, 10% infill).
Print "Box.stl" and "Lid.stl". I highly suggest the build plate be precisely trammeled before printing, and not too "tight" (e.g. print head not too close to the build plate).
Test fit and trim, file, sand, etc. both parts as necessary for smooth insertion and removal of "Lid.stl" into "Box.stl". Depending on the colors you chose and your printer settings, more or less trimming, filing and/or sanding will be required.
Assemble as shown in "Assembly.skp" or "Assembly.stl".
Feel free to comment if you have questions.
Hope you like it!
You fail only when you decide to quit learning.