Tlatelolco, Mexico City
 
In the beginning Tlatelolco was another marshy isle just north of Tenochtitlan. Some Aztecs decided not to follow the crowd and set up their own fiefdom here. Eventually there was a feud and when Tlatelolco's invasion of her sister city failed the latter put most of the rebels to the obsidian blade and virtually enslaved the rest by means of heavy annual tribute - a practice that eventually worked against them during the incredible set of circumstances of the (Spanish) conquest. Being a separate city it had its own teocalli (enclosed sacred plaza) with twin temples to Huizilopochetli and Tlaloc, but unlike Tenochtitlan most of the foundations of the buildings in virtually the whole teocalli are there to view and explore.

Due to the detailed description in his book, Bernal Diaz, a soldier in Cortez's army, enlightened posterity of Tlatelolco's reknown as a marketplace where goods from the entire empire were brought for trade. Fresh fish from present areas of Veracruz and Acapulo could be found here for instance. The transport activity of canoes on the lake and in canals alone was an unbelievable sight even for the conquistadors. This market was southeast of the teocalli and plaza where the conquerors decided to build their Iglesia de Santiago. Infamously the church became the school where young conquered Aztec nobles learned to revere their new religion and masters.

Since this transformation had its roots here, the remaining great plaza was dubbed Plaza de las Tres Culturas (Plaza of the Three Cultures) - those being Aztec (or indigenous), Spanish (or european), and the modern Mexican mestizo. Due to recent history the name of this plaza now evokes the sad circumstance of the 1968 massacre of hundreds of political protesters on the eve of the Olympic games.

A rather large area is now referred to as Tlatelolco such that many residents are oblivious to the existance of Aztec ruins hereabouts. Surprisingly, this large area, much of it once lake bottom, has residential appeal since quite a green belt of parks and plazas was planned during development.

Click on a picture below to blow it up!

If you take the metro to the Tlatelolco station, the ruins are east with a southerly bias, but there is quite a fine trail most of the way.
These two pictures are the first part of that walk.

Eventually you come to this walkway tunnel under the main north-south artery Lazaro-Cardenas.
Then right there before you looking east is the ancient teocalli of Tlatelolco.

Looking southwest across the teocalli. Looking southeast across the teocalli you see the Iglesia de Santiago.
The remnant of the templo major in front of the church (far right) would have been as high as the church at 114 steps (per Bernel Diaz).