Thanks hein! I already had found the info, but this site is VERY cool! Laurent, I'm essentially still trying to put it together. The shadow square wires are a problem, but you would think that they would be inconsequential, and unnoticeable considering the sheer size of everything, but Louis Wu did make at least one reference to seeing the glint of sunlight on them at one point. You had suggested this Challenge, and I was trying to think of subject matter, to no avail, and then one day I was at work and it suddenly hit me: "Ringworld!" Modeling the ring itself was actually quite easy, but the shadow squares were a problem, getting them placed right, but it's an absolute nightmare getting terrains on it, let alone cities..... I will have something to show for it soon. :)