The Fall of Teotihuacan
Teotihuacan was abandoned around the year 800, which is considered the end of the Mesoamerica's Classic period. The causes of the fall are not known, but it's possible there was a prolonged drought or an epidemic. It's also possible that there was a conflict with another group or an internal conflict: some of the buildings show evidence of destruction by fire, as opposed to merely being abandoned, like many of the Mayan archaeological sites.
The final stop on your tour of Teotihuacan: Enjoy the view from the Pyramid of the Moon.