In this flash program the 4-dimensional cube is mapped to a 3-dimensional object by just leaving the 4th dimension away. The resulting 3-dimensional cube is then mapped to two 2-dimensional images with slightly different points of view.
Click on the cubes to give keyboard focus to the flash program.
You have to focus the left cube with your right eye and vice versa, as implied by the small diagram. Now you should see three cubes: One in the center, that you are watching, and two on the left and right of it, which you should ignore.
Use the arrow-keys, optional with shift or ctrl, to turn the cube. (left, right, up, down, shift+left, shift+right, shift+up, shift+down, ctrl+left, ctrl+right, crtl+up and ctrl+down)