Perhaps my number one recommendation for a visit to Mexico City is to see one or more markets. There are major markets all over the city where people go to buy everything from fruit and veggies to clothes and toiletries.

Most markets also have an amazing butcher section. Don't seek that out if you are a squeamish vegetarian, but it is worth a look if you won't get sicked out. Huge cuts of meat, whole, skinned heads, whole bodies of large and small and generally unidentifiable animals. On hot days, flies everywhere.

Other than the general markets that are everywhere, almost always right near a metro stop, I especially recommend two:

1. Mercado Merced/Sonora (Metro Merced)
   Getting off the Metro at Merced, you are dropped off right into Mercado Merced. This is one of the bigger and definitely most vibrant markets you will see. There are sections for food and basics, and also a pet section, and a party decoration section. You will learn so much about real Mexican culture walking through this market! If you happen to go around a holiday there will be seasonal merchandise everywhere. In September, there are Mexican flag everythings all over the place-- jewelry, decorations, virgins of Guadalupe-- for Mexican independence day. No, it's not Cinco de Mayo, that is just the battle of Puebla. Mexican independence day is September 16. I will post more about that special day later.
   After you finish at Merced, cross over the street on a pedestrian bridge to Mercado Sonora. This is where Mexicans get all there witchcraft trappings, including herbs, amulets and even ant-witchcraft and anti-curse sprays. There is also a lot about Santa Muerte. She is something else you have to know about to really appreciate Mexico City... perhaps I'll post more on that later as well.
   This market could take you the whole day. If you eat street food (a personal choice-- I do but I have been here for a long time, and do have diarrhea all the time) the best food you will eat in Mexico will be in the markets, so get some tacos and a plastic baggie of juice and enjoy it.
2. Mercado Artesania, (Metro Balderas)
   If you are interested in buying any gifts or souvenirs, all types of artesanias are available here from all over the country. This is where most people that sell things in markets buy their goods, so you will get a pretty good price and see some very interesting things.

If you are the type of person who can squeeze gallons of experience out of just walking around and seeing everything, fill your eyes at the mercado.