The Voyage of the Dawn Treader and The Silver Chair - C.S. Lewis

A voyage to the very ends of the world. Narnia... where a dragon awakens... where stars walk the earth... where anything can happen. A king and some unexpected companions embark on a voyage that will take them beyond all known lands. As they sail father and farther from charted waters, they discover that their quest is more than they imagined and that the world's end is only the beginning.

 Eustace and Jill escape from the bullies at school through a strange door in the wall, which, for once, is unlocked. It leads to the open moor...or does it? Once again Aslan has a task for the children, and Narnia needs them. Through dangers untold and caverns deep and dark, they pursue the quest that brings them face to face with the evil Witch. She must be defeated if Prince Rillian is to be saved.