If you haven't seen it yet, check out this faithful reproduction in LEGO of my favorite Escher print.

I'm glad those guys made that: now I don't have to. (I started planning a model of Relativity years ago, but never started building it. It's a tempting subject because it's recognizably Escher but isn't actually physically impossible to build; furthermore Escher pretty obviously designed it using a sort of 3-D grid, so it translates well to LEGO or similar systems. I was going to use Linka, which I still think would suit the subject perfectly.)