Question Quest by Piers Anthony
Youth is wasted on the young.
Being grown up is a drag . . . or so thinks Lacuna, one of the mischievous Castle Zombie twins.
So she makes the Good Magician Grey an offer he can't refuse. Thirsty for a taste of the Elixir of Youth, she'll help him outwit the evil Com-Pewter, if he'll send her to Hell (in a handbasket, no less) to find Humfrey, the missing sorcerer. And while there, she'll learn the True History of Xanth (simplified) and help rescue a blushing Rose from the demon X(A/N)th . . . with the help of a gorgon or two.