This megalopolis of 20 million people is an intoxicating blend of ancient and modern. Unique ruins conjure the Aztec period, while charming Old World architecture recalls Spanish colonial times.

1. To navigate this labyrinth in a timely manner, hire a guide/driver at a cost of about $25 an hour. Begin your tour at the Presidente InterContinental Hotel (Campos Eliseos 218, tel 5255 5327 7700). Located in the upscale Polanco area, it’s a favorite among business travelers.

2. Pay attention as your driver maneuvers along Paseo de la Reforma. This grand avenue is lined with monuments that pay tribute to Mexico’s history. Stop at Zocalo, the city’s main plaza and the second-largest square in the world after Moscow’s Red Square. The Aztecs settled here in 1325. Today it’s the site of magnificent examples of colonial architecture.

3. Walk across the square to the National Palace. Inside you can visit the famous murals by Diego Rivera that depict Mexican history from the time of the Aztecs to the Mexican Revolution. It was in the courtyard that Hernando Cortès held the first bullfight in 1526. (Open daily, 9 a.m. to 5 p.m. Palace admission is free, but you’ll need a photo ID.)

4. When you leave the palace, turn right and walk toward the imposing Metropolitan Cathedral (open daily, 10:30 a.m. to 2:30 p.m.) to feast your eyes on an amazing blend of Baroque, classical and neoclassical styles from the 16th century. This is the largest cathedral in the Western Hemisphere.

5. Just behind the cathedral is the Templo Mayor, the ruins of an Aztec temple that workers accidentally discovered while digging the foundation for the city’s subway in 1978. Adjacent to the ruins is a museum (open Tuesday to Sunday, 9 a.m. to 5 p.m.) filled with artifacts from the Aztec period.

6. Head back uptown, making a quick detour at Plaza Garibaldi to encounter Mexican culture in the form of a mariachi serenade. This is where locals come to sample mariachi bands before hiring one to entertain at a party.