The Forbidden Places And Subterranean Secrets Of 10 Big Cities

There is more to a city than meets the eye - for what we see, what we know of a place, is often but a narrow cross-section of the complete organism. Like the layers of an onion, so too are our urban environments built upon layers and layers of infrastructure; from drains and sewers, to cable runs and metro lines.
Some cities conceal the remains of ancient civilizations, while others hide more recent interments. Here is a look at 10 cities from around the world, and a sample of the subterranean secrets each one keeps.