The Mayan ruins at Cobá differ from most of the others available for tour in the Yucatán in that they've been completely overrun by jungle. In this picture, there's even a full grown tree coming out of the middle of the restored wall. The ruins available for view have been hacked out of the jungle in a few spots, but according to aerial photography–and what you can see as you walk around the enormous site–there are still 6000 structures that have not been rescued from the jungle. Those you can see have been mostly reconstructed from piles of rocks left by the ferocious attack of 500 years of trees and vines.