Mexico City is the teeming capital that people crave for an active vacation. Though it's the largest city in the world, with more than 20 million people, it's composed of intimately scaled areas, making it an approachable destination. The city itself is built on top of the ruins of the ancient Aztec capital of Tenochtitlan, hints of which can be seen in some areas. 
Getting there: Benito Juárez International Airport (www.aicm.com.mx, 011-52-55-5571-3600) is served by Aeroméxico (www.aeromexico.com) and most major U.S. airlines, including Delta Air Lines (www.delta.com), American Airlines (www.aa.com), United Airlines (www.united.com), Northwest Airlines (www.nwa.com) and Continental Airlines (www.continental.com). The airport is 30-45 minutes from many major hotels, and several can arrange for a car to pick up your client at the airport.
Getting around: Most major car rental companies are here, too. If your clients decide to drive, recommend a GPS-enabled vehicle. The streets do not follow a grid pattern and can be confusing. For taxi service, have your clients request a cab be called by someone from the attraction they are visiting. Cabs that are not government-approved can be dangerous. 
Tour operators: Slatterys Escorted Tours (www.slatterys.com) operates in Mexico City and beyond, with the goal of letting travelers experience the traditions and cultures of the community. Caravan Tours (www.caravantours.com, 800-CARAVAN) combines Mexico City with other historical cities such as the ruins of Teotihuacán. City Discovery (www.city-discovery.com, 419-244-6440) offers a variety of day and night trips in and around the city. Majestic Mexico Tours (www.mexico-tours.com, 850-314-9339) has three-and six-day packages, which include hotel transfers and sightseeing.
Lodging: Most luxury hotels are on the city's main street, Paseo de la Reforma. Here's where you find the 240-room Four Seasons Hotel Mexico (www.fourseasons.com/mexico, 800-332-3442). The hotel restaurant, Reforma 500, specializes in contemporary Mediterranean cuisine. Agents should contact director of sales and marketing Sakari Malinen ([email protected], 011-52-55-5230-1818, ext. 1446). Another upscale hotel on the Reforma, the 237-room W Hotel Mexico City (www.whotels.com, 888-625-5144) resonates with the high style for which the W line is known. Minimalism combines with spa influences at the W, which is near Chapultepec Park. The hotel has an indoor Koi pond, full-service spa and a Rande Gerber-created lounge. The signature restaurant, Solea, serves steaks and seafood. Agents should contact sales and marketing director John Freudenthaler ([email protected], 011-52-55-9138-1820). 
A newcomer to the Reforma, opened in the last year, the Embassy Suites Mexico City Reforma (www.embassysuites.com) is an American all-suite hotel with an Argentinean steakhouse, Evita, that serves private-label wines. Agents can speak with director of sales Sinaí Sánchez ([email protected], 011-52-55-5061-3004). The 209-room Marquis Reforma Hotel (www.marquisreforma.com, 800-235-2387), which belongs to The Leading Hotels of the World, bears a postmodern design. Most of its accommodations are suites. It contains restaurants overseen by a James Beard House-honored chef, Ignacio Gutierrez, and the largest spa in the city. The Marble Spa features 11 treatment rooms, Jacuzzis, steam bath, sauna, a panoramic pool, beauty parlor, Swiss shower and fitness center. Contact Yolanda Pi????spa director, at 011-52-55-5229-1200.
Attractions: Recommend a private tour at the Frida Kahlo Museum, because all its signs are in Spanish. With a personal guide and translator, clients can better understand the artist's experience. Many of the museums also have handheld devices that serve as tour guides and are available in a variety of languages.
Dining: There are so many good restaurants in Mexico City, yet for some reason it's not on most travelers' top list for food. Tipping here is about 10 percent, but leaving 15 percent will make your client seem like a big shot.
Casa Lamm (011-52-55-5514-8501) is adjacent to an exclusive private school and arts center. One wall of the restaurant is made up entirely of retractable glass doors, with views of a picturesque courtyard. It's recognized as one of the city's top dining spots by multiple magazines. It's at Alvaro Obregon 99, in Colonia Roma.
In Coyoacán, Los Danzantes (www.losdanzantes.com, 011-52-55-5554-1213) serves contemporary Mexican cuisine. Suggest the fresh tuna in garlic and chili or the Oaxaca two moles chicken. Address is Jordan del Centenario 12.
Los Girasoles (www.restaurantelosgirasoles.com, 011-52-55-5510-0630) off Plaza Manuel Tolsa features seasonal dishes and cuisine that explore traditional Mexican flavors and textures.
Around the corner from the Embassy Suites is Tacos El Caminero, an authentic local joint with counter seating, where Coca-Cola comes in little bottles and a television airs soccer matches. It's a great place to get a taste of real Mexican culture.
Entry requirements: New rules mean that a passport is now required to enter and leave Mexico from the United States. A visa is not necessary.
Other tips: High atop Mexico's central plateau, Mexico City is about 7,000 feet above sea level. That translates into weather that's mild all year long, with high temperatures ranging from 70 to 80 degrees. Lows usually fall into the 40s and 50s, so a jacket is important. From June to September, it typically rains for a bit in the afternoon. October and May are the best months to avoid downpours.
Mexico City is in a major earthquake zone. In 1985, a quake of 8.1 magnitude proved to be one of the worst ever in this hemisphere. The last earthquake of note occurred in summer 2006. Suggest clients take note of quick ways to exit a building, just in case.
Also, tell them not to worry if they're rusty with their high school Spanish; most people they will encounter should speak at least some English. As for money matters, the exchange rate at press time was just under 11 pesos to one dollar.
Warn clients that this is a smoking city, both indoors and outside. Locals will not be happy if asked to extinguish their cigarettes. —GH