Did you know that... A hundred years ago Chicago had a miniature underground train system that criss-crossed beneath the streets, delivering coal and other materials? The trains could go right into a building's basement. Even today, few people know these tunnels exist.... Or that Paris has over six million skeletons buried in ancient chambers and tunnels beneath the city? The ancient Romans first dug up this spot while mining for rock, but 200 years ago the overcrowded city of Paris needed new space to bury its dead. Hidden Worlds presents 11 intriguing stories of extraordinary tunnels past and present from around the world. This fascinating book will introduce you to nature's tunneling mammals; the ancient Greek myth of the Minotaur in the labyrinth; the aqueducts of the ancient Romans; the hidden treasure in the pyramids of Egypt; the great escape of WWII prisoners of war...and much more! Richly portrayed with large cartoon-style illustrations and informative yet wickedly funny captions, the stories in this original collection make for a riveting read. You'll be amazed at the interesting facts you'll unearth. An introduction provides an overview of the hidden world of tunnels, the varied reasons why people have constructed them since ancient times, and how they have done so. A special chapter at the end of the book provides more detailed information on each story. Additional resources, such as websites, are included. An index will help locate specific places and events in the book, making this a useful reference tool for young students.