A cube can unfold its six sides as though on hinges so they stay connected even when flattened out. They can form any of 11 different shapes. See the image below. These outlines are pentomino shapes, part of the set of 12 shapes made of 5 squares each. Rick's genius inspiration was to find a path along which a cube can roll, unfolding itself into its 11 shapes and leaving behind the pentominoes footprints. Click on the image to watch this closed-path "walk" animation on Rick's site and be amazed.
 

Then check out our full polyominoes and polycubes section for all the hands-on ways they can challenge your puzzle-solving ingenuity.