Oddly, this was always one of my favorite books in the series as a child. When rereading as an (agnostic) adult, it lost much of its appeal. 
 C.S. Lewis continues his allegory of Christianity to the next logical step: the end of the world. The main characters here are actually some of the creatures of Narnia rather than the children, and Puzzle, the donkey, was always one of my favorites. Even as a child, I found Lewis's picture of heaven to be...well...boring. But he certainly captures beauty and longing that are so much a part of the true believer's faith.