Kind of a meh question for me, but here's a second-hand purchase that was kind of fun. I found this at a used book store, filed with travel books and maps from real places. I don't know if the shop owner didn't know or just didn't care what it was. Anyway, I was still a kid and the fact that it was only $1.95 was a big plus. This is actually still my preferred World of Greyhawk reference. The others all filled in details that I had already made up for myself, and of course there's that irritating thing where they insist on moving the date forward and including the effects of events that didn't happen in my campaign.