Virtual Ball

An autostereogram gives the optical illusion of a three-dimensional image, based on a normal two-dimensional image. Please google on 'autostereogram' or 'magic eye' for more info.

I wondered whether it was possible to make a 3D printed autostereogram. This thingy proofs it can be made and that it works. :-)
If you print the attached thingy in two different colors (by pausing at 1 mm height and changing filament), you'll get a usable sterogram. It is optimized to viewed from 25 - 30 cm.

Note: not everyone is capable of seeing the hidden object in an autostereogram. When in doubt about that, download an arbitrary autostereogram first and try to see it on your monitor.