The Menger sponge is a fractal curve that was first described by Karl Menger while exploring the concept of topological dimension. It is described by an iterative algorithm. It begins with a cube that it is sub-divided into 27 small cubes, like a Rubik’s Cube. The inner 7 cubes are removed, the cubes in the middle of each face and the cube in the very center. The result is M1. The process follows with each small cube ad infinitum.
The drawing corresponds to M3, the third iteration. If we consider small cubes for making the sponge, it should be needed 203 = 8000 cubes (20n where n is the number of iterations performed on the initial cube).