Recently visited this site - before it made the list and consequently information at the site is pretty thin on the ground. The structure is quite impressive, and the length is even more so. I visited probably the most impressive bit - same picture as previous poster has put up. Getting here, as long as you have your own car is quite straightforward, and it was on our way from the coast to Teotihuacan. See this place in the evening, then night stop at Teotihuacan and then as long as it sin't a weekend get to see the pyramids all on your own at 08:00.

Hopefully now being added to the site they will do something to clean up the river passing through the valley - just needs a bit of tidying really. there were lots of locals there, picnicking and a few on horseback, not sure why they were there.