This was most of my day. A Menger sponge is a three-dimensional fractal shape, where the middle of each face of a cube is removed like in the origami shape here and then each of the remaining 20 cubes are reduced in the same way, and so on ad infinitum.
A cube has six faces. This origami shape has 72. The next shape in the series has over 1000. I have a scary urge to try to make it. In a quick not-even-back-of-the-envelope calculation, it wouuld take me about two months.