Mexico City has one of the busiest subway systems in the world, carrying about 5 million people a day. Having lived and used public transportation in New York City, the first thing I noticed about the Mexico subway system is that it is very clean. On several trips I found the cleaning crew sweeping the corridors and train cars. Aside from food stalls and small shops, underground art can be found in stations. This one at the Instituto del Petróleo had two massive sculptures of bright orange barrels. The stations are also identifiable by their unique “logos,” and for this particular station, it was an oil well. Travel tip-- avoid the subway on Saturday when it becomes very crowded.