I made a simple 3D puzzle that has similarities to the cover of Douglas Hofstadler's cult 1979 book Gödel, Escher, Bach: An Eternal Golden Braid, which features two unusually carved cubes whose shadows spell out GEB and EGB. It occurred to me that the software I'd used, TinkerCad, could perform the same trick with any shape and that TinkerCad has a built-in character set. I tried using it to reproduce Hofstadler's GEB cube, and 5 minutes later I had the shape and an hour after that a small print. This tutorial will show you how to do it for any set of 3 characters or shapes.*
I recommend checking out 3D Modeling and Printing Your Own Shadow Cube by printeraction, which is very similar to this tutorial but more sophisticated as it eschews the TinkerCad character set and shows how to make a shadow cube from scratch using either TinkerCad or Fusion360.
* it's not quite that simple. Some letters don't play nicely together - if you try this trick with characters that are less substantial, it often won't work. So B is excellent but an unmodified I is terrible. The GEB cube is particularly good because all three letters do a good job of filling each face.
TinkerCad runs in your web browser and allows you to quickly create 3D plans. Go to https://www.tinkercad.com/ and sign up for an account. Click on "Create New Design".
Drag 4 red cubes on to the build area. They will all be 20 × 20 × 20 mm by default; that's fine for our purposes. You can always resize it later if you want it bigger or smaller.