Calixtlahuaca Archeological Zone is 8 km (5 mi.) n. on Mex. 55 to the site turn-off, then about 3 km (2 mi.) w. The site is located on a hilltop above the village of the same name. Not much is known about its origins, although it was taken over by the Aztecs around 1476. Several buildings have been uncovered: the conical Temple of Quetzalcóatl-Ehecatl; the Pyramid of Tláloc; and the Altar of Skulls (Tzompantli), which was probably used for human sacrifice. Buses make frequent trips from Toluca to Calixtlahuaca; there is a short uphill walk to get to the site entrance.