Get a rare glimpse into places that are usually out of sight! The Underground Worlds series uses detailed cutaways and illustrated diagrams to show the layout and purpose of various underground structures and systems. Find out how they were designed and built, the Challenges they presented in construction, and the innovative technologies that have made building underground possible. A comet that his Earth 65 million years ago created a huge crater in what is now Mexico. The impact also created cracks and holes that filled with rainwater, forming the largest underwater cave and longest underground river on the planet. Earth's Underground Structures uses cutaway illustrations to examine some of the world's most interesting underground structures, such as fault lines, caves, and volcanoes, created by Earth's natural processes. Book jacket.