Some of the more random things to see in mexico city go back
"Arbol de la noch triste".

The tree of the sad night, is apparently where Cortes had a little cry as he was fleeing the city and watching his men getting slaughtered by the Aztecs. He pulled himself together quite quickly though, and came back and took the city not long after. There's not much to see, it is in a random part of town on the Mexico-Tacuba road near metro Popotla.