I was fascinated to see this clip, by National Geographic, showing how new technologies are aiding in the discoveries of long abandoned Mayan cities.
Check out this short videoclip. (takes a minute to load so be patient)
I've always been amazed at how completely the jungle has taken over these areas, which were thought to have been extensively deforested during their time. I visited Tikal over 25 years ago and it's obvious the Mayans were a very advanced civilization.