The Silver Chair by C.S. Lewis
Narnia...where owls are wise, where some of the giants like to snack on humans, where a prince is put under and evil spell...and where the adventure begins. Eustace and Jill escape from the bullies at school through a strange door in the wall. Aslan has a task for the children, and Narnia needs them. Through dangers untold and caverns deep and dark, they pursue a quest that brings them face to face with the evil Witch. Enter this enchanted world in The Chronicles of Narnia.
The Chronicles of Narnia, Book #6