Reachable only on foot and covering 8 sq km, the remains of this pre-Hispanic settlement have been only partially excavated. It shows Olmec, Huastec, Totonac and Toltec influences and its history spans more than 1500 years, from BC 100 to AD 1500, though its heyday seems to have been between AD 1200 and 1500. It's 2.5km away from the El Cuajilote site, where you can get directions.
It's not as visually impressive as its sister site; there's a small ball court and some residential buildings, but the underlying idea is mindblowing. It is possible that the yet-to-be-excavated ruins are considerably more extensive than currently believed, and that the complex civilization that flourished here played a considerably more prominent role in terms of Mesoamerican trade and influence than previously believed.