It comes into view overhead, bigger than the biggest, most unpleasantly-armed starcruiser in the imagination of a three-ring film-maker: a turtle, ten thousand miles long. It is a Great A'Tuin, one of the rare astrochelonians from a universe where things are less as they are and more like people imagine them to be, and it carries on its meteor-pocked shell four giant elephants who bear on their enormous shoulders the great round wheel of the Discworld.

A world like that, which only exists because the gods enjoy a good joke, must be a place where magic can survive.