|This cube also floats, but no illusions here.|
The above video is from Peter Dahmen's site (translated using Babelfish)>>
He also provides a PDF file so you can make your own, here (opens a PDF)>>
Here's another take on the same cube design:
These illusions mess with our idea of what we should be seeing. We see many more examples of solid cube shapes than we do of the structure eventually revealed in these videos, so we're deceived into assuming that what we're seeing is a cube.