The Lamp-post Library
Since the first episode, Phil and Daniel have always acknowledged their role as novice guides through literature. The following books are great ways to extend your stay in Narnia, Middle-earth, and other fantasy worlds; they are authored by academics, theologians, and critics.
C.S Lewis Goes to Hell: A Companion and Study Guide to The Screwtape Letters, by William O'Flaherty
Further Up & Further In: Understanding Narnia, By Joseph Pearce
The Keys to the Chronicles: Unlocking the Symbols of C. S. Lewis's Narnia by Marvin Hinten
King Arthur and His Knights of the Round Table, by Roger Lancelyn Green
The Medieval Mind of CS Lewis: How Great Books Shaped a Great Mind, Jason M. Baxter