Megacities takes a revolutionary look at the places where most of us live: the modern metropolis. The key to a city's survival is its vital organs - power grids, transportation systems, water supplies, air traffic control and countless others. Behind each system that we take for granted lies the huge infrastructure of a mega city. Visit eight iconic cities around the world: Las Vegas, Mexico City, Hong Kong, London, Paris, Sao Paulo, Mumbai and New York.