Few of the modern visitors to Teotihuacan are aware of the vast and mysterious underworld of caves and man-made tunnels that extends under much of the ancient site and for miles around. The existence of these tunnels has been known for centuries, but not even the most recent research has been able to solve the mystery of their origin and purpose. Very much like at Giza, in Egypt, these tunnels are rumored to connect all the main pyramids by means of underground passageways, and perhaps even lead to the records of a lost civilization.