This is not to be missed if you are visiting nearby Cuernavaca or Taxco. I enjoy these ruins more than Teotihuacan, outside of Mexico City. At one time as many as 20,000 people lived here before 1000 AD. Xochicalco (means in the house of Flowers in the Nahuatl language) still has ruins of temples, defensive walls and large ball courts. Built on a hill, tunnels were dug for transportation and defense. Don't miss the museum on the site.