Joe D.
Yelp
This is a spectacular pre-Aztec, even pre-Toltec (so pre-pre-Aztec and pre-pre-pre-Columbian) ancient city. At its height it had a population of 125,000, making it the 6th largest city in the world at the time. The city dates from the first century AD. No one really knows much about the civilization that built it, because so many later waves of civilization came after and assimilated the various influences. The extreme modern tackiness allowed at the site insults Mexico's history and almost destroys the experience.
There are enormous stepped pyramids which directly influenced later culture and civilizations in Mexico and Central America, even as far south as the Incas in South America. The town is anchored by Pyramids of the Sun and Moon, each at the end of a long axis, flanked by imposing ruins. Most of the"public building" area of the town has been excavated. The suburbs and home sites are still being uncovered. Interestingly enough, many of the residences are multi-story apartment buildings. From the first century and onward, this was quite a densely populated, cosmopolitan place. Every later Meso-american civilization tried to claim this spectacular heritage as their own. Even today the Teotihuacan Pyramid of the Sun is featured in everything from beer labels to soccer team logos.
Bring good hiking shoes, sunscreen and a lot of water (anything you forgot will be hyper-expensive nearby). The steps going up the pyramids are steep but well worth the climb. Tour guides are not required, but a good idea. Just try to forget that some fairly gruesome things they describe happened on the steps and platforms (priests with obsidian knives on their fingers slicing into war captives' chests to pull out their beating hearts, etc). Even without the tour guide, you get the idea from the gargoyles and contorted screaming figures carved on the balustrades.
One incredibly irritating drawback is the wild modern commercialization of the site. There are hyper-aggressive vendors INSIDE the archeological zone. It's hard to walk 10 feet without being offered a t-shirt or trinket from a guy or gal who just won't stop. I'm an easy mark for trinket sales, BUT this was like being hassled to buy a print of the Mona Lisa in a bikini INSIDE The Louvre.
The site itself has been highly compromised. Given Mexico's loose historic protections, there is a local Walmart you can see from the pyramids. To add insult to injury, there is a Vegas-style cartoon character light-show for tourists. Walt Disney would be proud, Montezuma would not.
I gently asked the on-site manager why this was allowed and mentioned calmly that it really ruined the experience. He actually laughed and said "que quieres beber gringo grunon"(what do you want to drink, ya grumpy tourist). He was pointing to the on-site, very cheesy and overpriced bar-restaurant. Gee, I think this might be a management problem.