This is a level 2 Menger Sponge made of business card cubes. I made it over the course of about 6 months while working as a telephone technical support engineer back in the late 90's. Eventually I paneled the whole thing to make it smooth, but never got around to taking pictures of it after these. The cube was on display in the lobby of our company for several months, but didn't survive the move to new office space.
There are other examples of level 2 card cubes on the internet, but The one made by Dr Jeannine Mosely, is the only level 3 card cube that I'm aware of. It took nine years to build!