The Thieves' World series of over a dozen novels set in a shared world, conceived of by Robert Lynn Asprin in 1978. The series has also led to a series of graphic novels, a roleplaying game, and a board game.
1.
A Notable Guide to Thieves' World
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A guide for all things dark and dangerous that lurk the city of Sanctuary from the Thieves' World novels, edited by Robert Lynn Asprin.