Currently reading Strata, by Terry Pratchett. Or re-re-re-reading, since I've read it three times before. This was Sir Pterry's third novel, first published in 1981, and features an artificial flat Earth two years before his first Discworld novel. If you're a Pratchett fan who has mostly read Discworld, it's worth seeking out Strata. This one is science fiction rather than fantasy but you can see him exploring some of the same ideas that later recurred in the Discworld series. Or if you've never read anything by Pratchett, read Strata anyway. It's wonderful. This is a 1983 paperback edition I found in a used bookstore in the early 90s.