The Color of Magic by Terry Pratchett
In this, the maiden voyage through Terry Pratchett's divinely and recognizably twisted alternate dimension, the well-meaning but remarkably inept wizard Rincewind encounters something hitherto unknown in the Discworld: a tourist! Twoflower has arrived, Luggage by his side, to take in the sights and, unfortunately, has cast his lot with a most inappropriate tour guide—a decision that could result in Twoflower's becoming not only Discworld's first visitor from elsewhere . . . but quite possibly, portentously, its very last. And, of course, he's brought Luggage along, which has a mind of its own. And teeth."
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