Steel, 3” cube
The canonical fractal in which you divide a cube into 27 cubelets, knock out the center and six face-center cubelets, then recurse on all surviving cubelets. This model has four generations, and it looks like a bit of computer graphics that's somehow escaped the screen.
I was able to produce these for about 18 months after metal printing launched. They were quite popular, then one day the technicians at Ex One wised up and realized that spending all of their time poking tumbling media out of tiny square those holes was a poor life decision.
I've never done much more with fractals. I don't like the way they run into the resolution limits of 3DP. I'm sure there are great thing to do with them, but they need their own expert. I'm more interested in topology.