Located at an altitude of 7,000 feet, Mexico City is a place of extremes. With a metro population of 21 million, it has some of the world’s highest and lowest standards of living. The city’s foundations were laid by the Aztecs in 1325, and today the Museo del Templo Mayor displays the magnificent ruins. The Zócalo in the historic downtown is one of the largest civic squares in the world, surrounded by colonial churches and Aztec pyramids. A slew of excellent museums could fill a traveler’s itinerary for days. Highlights include the Museo Nacional de Antropología and Museo Frida Kahlo. The city’s notorious air pollution has abated, but whether it is aggravating or barely noticeable will depend on the day. Although the city makes for a thoroughly rewarding travel experience, visitors should exercise caution, avoid taxis — Uber provides a safer alternative — and engage the services of a reputable guide.