I like this graphic -- first of all it is a 'gif', an elegant and long neglected graphical format and secondly it illustrates a very difficult concept to explain -- a 4-dimensional cube.

As John Baez explains "Let's do a bit of 4-dimensional geometry. Here's a movie of a rotating 4d hypercube, also called a tesseract. Of course it's projected down to 3d space, and then drawn in perspective on your 2d computer screen. But notice that just as a cube consists of 2 squares with edges drawn from the corners of one to the corners of the other, this consists of 2 cubes with edges drawn from the corners of one to the corners of the other."