We spent a good five hours exploring the full extent of the inscribe area. Teotihuacan is a place that you should consider careful planning. Don't mistake the Pyramid of the Sun as being the only highlight of this huge complex. Arriving early will pay off, especially entering before large numbers of tourists arrive by bus and vendors set up shop. Teotihuacan is vast.
1,000 years Before the Aztec
Mysteries remain about the origins and even name of the Teotihuacan Civilization. Consensus remains allusive on various aspects of daily life at Teotihuacan, but this early civilization's influence is undisputed.
Contemporaries With the Classic Maya Period
The Teotihuacan Civilization's relationship with various Mayan City-states remains a topic of debate. Yet, historians tend to agree that there was some interchange of culture and trade between them.
Contemporaries With the Hopewell Culture
While little if any evidence exists of awareness of each other or any direct connection, I find it interesting that the zenith of both cultures were nearly identical. This provides a small insight into the civilizations on the North American continent in the 5th century.

The best view of the site, is without a doubt from the Temple of the Moon looking out over the Avenue of the Dead and the Pyramid of the Sun. Nearby, is a ruined palace site that includes original and restored paintings of this ancient Mesoamerican culture.
Seemingly, an inevitable tourist activity (pre-2020) when visiting Teotihuacan is hiking the Pyramid of the Sun. The view is certainly special and the climb makes you appreciate the size and labor involved in its construction.
I enjoyed my time visiting this site and it should not be missed by anyone who visits Mexico City. On a side note, the Aqueduct of Padre Tembleque is located near Teotihuacan. At this point I know of no easy way to visit both WHS using public transit in one day. Yet, I am sure this will eventually become a reality within our community of resourceful travelers.
Flickr Album