““How thick is the Earth’s crust, Perry?” I asked. “There are almost as many conjectures as...”
Built in the 1970s as a bomb shelter, the underground city of Dixia Cheng in Beijing, China, is often referred to as the Underground...
Did You Know?
A seventh-century BC underground city discovered in Derinkuyu, Turkey, was found to contain stables, schools, chapels—even wine and olive presses. It had a 55-meter...