The City Green: Exploring the Urban Eco-Reserve of Xochimilco

Mexico City may be a sprawling metropolis of 21 million, but on its edge is an oasis of green unlike any other in the world. Known as Xochimilco, it is the last part of the city that preserves an ancient system of canals and farms first built by the Aztecs when the area was on the edge of a long-gone lake.