Piers Anthony & Piers A. Jacob 
Xanth 14: Question Quest [EPUB ebook] 

Youth is Wasted on the Young Being grown up is a drag . . . or so thinks Lacuna, one of the michievous Castle Zombie twins. So she makes the Good Magician Grey an 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 Humphrey, 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) . . . with the help of a gorgon or two.