The Pilgrim's Regress by C. S. Lewis

The first book written by C. S. Lewis after his conversion, The Pilgrim's Regress is, in a sense, the record of Lewis's own search for meaning and spiritual satisfaction—a search that eventually led him to Christianity.

Here is the story of the pilgrim John and his odyssey to an enchanting island which has created in him an intense longing; a mysterious, sweet desire. John's pursuit of this desire takes him through adventures with such people as Mr. Enlightenment, Media Halfways, Mr. Mammon, Mother Kirk, Mr. Sensible, and Mr. Humanist and through such cities as Thrill and Eschropolis as well as the Valley of Humiliation.

Though the dragons and giants here are different from those in Bunyan's Pilgrim's Progress, Lewis's allegory performs the same function of enabling the author to say simply and through fantasy what would otherwise have demanded a full-length philosophy of religion.