"There are only twenty million of us!" a friend of mine from Mexico City said to me one day not long ago. That number -- which is still rising -- puts Mexico City among the great cities of the world.

Mexico City has enough tourism sites to keep you busy indefinitely! Museums, art galleries, sports teams of all sorts, great shopping, a beautiful historic downtown area, wonderful parks... there is no limit to the things you can do in Mexico City. Here are a few:

The Museum of Anthropology is famous worldwide for its extensive collection on Mexican archaeology and history.

The Bosque de Chapultepec is a huge park in the city, with many things to do within it: museums, cafes, etc. And the people-watching is great.

In the downtown area, the Zocalo is one of the largest plazas in the world, with the cathedral, the presidential palace, and much more in the vicinity. Beautiful historic buildings!

The floating gardens of Xochimilco

Art, including great murals and paintings of Diego Rivera, Frida Kahlo, and many others

Before you pack your bags for a vacation there, do consider pollution, congestion, and crime.

Pollution: The air quality is terrible, as the geography of the valley that Mexico City sits in combines with the heavy traffic to create a thick stew instead of the air your lungs would prefer. At about a mile high, the city's air is thinner to begin with anyway.

Congestion means that travel around the city is slow and tedious. The traffic is so frustrating, and parking so difficult, that rental cars aren't generally recommended. See more on the page about travel to Mexico City and within it.

Crime: In the 1990s, Mexico suffered economic problems that left many of its people destitute. Some of these people used a lot of ingenuity in figuring out ways to separate richer people from their goods. Today, tourist guidebooks on Mexico generally explain the situation in detail. Here are some general guidelines: Carry little cash with you, and be very alert to your surroundings. Stay out of places where there are few people. Don't necessarily trust the police, as in some cases they are involved in crime too. Don't hail a taxi on the street, as some of the roaming cab drivers are involved in robbery. Taxis at your hotel or in official cab stands are much better. While other parts of the country may have seen some increase in crime, it's in Mexico City that it's reached the highest levels. All in all, a hefty dose of thoughtful preparation (making photocopies of your passport, leaving your fancy jewelry at home, that sort of thing) and vigilant common sense are called for.

But do these drawbacks mean you should avoid Mexico City as a tourism destination? It all depends on what you want. Many people love the vibrancy of the city. There may be something you particularly want to do or see there. You may love big cities and want to experience the unique flavor of this one. But if you are just looking for a laid-back, relaxing vacation, you will be happier somewhere else in Mexico. People go to Mexico City for business. With about a quarter of the entire population of Mexico, and with government and industry offices centered there, "the city" (la ciudad) as it's called, is where a lot of things happen. Many of the hotels in Mexico City offer suites for business travelers to use as offices while they conduct their business.

If your business takes you there, or if you decide to live or retire there, you will do the same thing that most of the other twenty million do: make the best of any drawbacks and enjoy the many wonderful aspects of the city. If you might be there for a long time, see the page on real estate in Mexico City.

I've been there several times, and I have happy memories of fascinating hours in the Anthropology Museum, international restaurants, staying in ultramodern hotels and in intimate little places, the friendliness of people I met, and much more. I will spare you my unhappier memories, but none were really bad. It's unlikely I will return, as nowadays I like my cities on a smaller scale. But everyone's tastes are different, and you may love it. It's truly a phenomenon, Mexico City!

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Rosana Hart has traveled to Mexico many times. Her website, www.mexico-with-heart.com, contains the full text of a book she wrote about traveling in Mexico, as well as information and travel tips