Consider other books set in Middle-earth, such as The Lord of the Rings trilogy and The Silmarillion by J.R.R. Tolkien. Much can be made of comparing the original novels to Peter Jackson's popular film adaptations.
Consider other fantasy epics with extensive world building, such as A Song of Ice and Fire by George R. R. Martin.
Tolkien was a friend and colleague of C.S. Lewis, and their fantasy worlds were created in dialog with one another. Compare Middle-earth to Lewis's Narnia. Students may also wish to compare Middle-earth to other notable and well-developed fantasy worlds such as Neverland, Wonderland, Oz, and Lyra's world.