Dating back 2,000 years, the city was once thought to support 125,000 people, making it one of the largest urban centers in the world at that time.
Despite its grandeur, little is known about the civilization that built the pyramids at Teotihuacan.
By the time the Aztecs discovered the city, it had already been abandoned for hundreds of years.
Today, modern technology including radar and robots are slowly lifting the veil on the mysterious history of a lost civilization.
The Pre-Hispanic City of Teotihuacan became a World Heritage Site in 1987.
Click here for the full list of UNESCO sites Dave has visited during his travels.