At nearly 9 million, Mexico City is the biggest metropolis I've ever visited. I only saw a small chunk of it in my time working in el Destrito Federal, but it was almost overwhelming. (Seattle proper, my town, for example, is only 600,000-plus.)
Every inch of this city seemed to be alive. There were traffic jams everywhere. People on every block. It was fascinating.
Here are a few pictures of my time there, as a co-worker called it, el Defectuoso.