Square of the Three Cultures. Important historic landmark, containing a prehispanic pyramid, colonial church and modern apartment buildings. Part of the Tlatelolco complex, was the site of the 1968 Tlatelolco Massacre; a large crowd of students were shot by government-mandated troopers.
Wikipedia article:
http://en.wikipedia.org/wiki/Plaza_de_las_Tres_CulturasCategory:
square historic las colonialism massacre interesting place