Can I just say that I think I drew a pretty good Ringworld? Not to scale, I grant you, but still pretty good.

Ringworld was one of the first sci-fi books I ever read, and it's still one of the best. The whole Known Space series of stories and novels is just a blast - Larry Niven was clearly having a great time universe-building. And his characters are just so smart. One of the few fictional universes in which I wanted - and still want - to live.