A Menger sponge is a mathematical invention, a kind of fractal structure. To create one in 2 dimensions, divide a square into 3x3 sections, remove the middle section, then do the same for each remaining section: divide into 3x3, remove middle section, and so on. Doing that n times make a level-n Menger sponge. Menger sponges aren't limited to a plane. They are equally well-defined in 3D or even higher dimensions. The best part is that you can really see one: The Institute for Figuring is currently exhibiting a real, 3-dimensional level-3 Menger sponge built by Dr. Jeannine Mosely and a team of volunteers. Dr. Mosely has a degree from M.I.T., works in 3D modeling, studies computational Origami, and has created this Menger sponge completely out of folded business cards! Now why didn't I think to do that? Facts about the business card Menger sponge:66,048 business cards dimensions 54"x54"x54" weight 150 pounds time to build: 9 years! Dr. Mosely and the Menger sponge: If you are geeky enough (like me) to think this was a worthwhile project, here are some more photos you can admire.