Stephens John C. Stephens 
Journeys to the Underworld and Heavenly Realm in Ancient and Medieval Literature [PDF ebook] 

Concepts of heaven and hell are among the oldest, most widespread religious beliefs in history. In Western literature, they are frequently embedded in stories of underworld explorations and celestial journeys–stories examining the nature of the universe, life on earth and the existence of the gods. The author analyzes tales of wonder in both ancient and medieval European literature. Other-worldly narratives appeared in literary contexts in the ancient world, including mythology, poetry and philosophical writings. In medieval times, they remained a popular form of literary expression. These stories are primarily religious in nature, describing fantastic worlds filled with miracles and supernatural beings.