Huge, densely populated (more than 23 million including outlying districts), and highly elevated, Mexico City is literally intense enough to take your breath away. Icons such as Plaza de la Constitucion (also called the Zocalo) and the Catedral Metropolitana (Metropolitan Cathedral) are massive in scope… but interestingly, so are the green spaces. Bosque de Chapultepec (Chapultepec Park) is 1,600 acres, with a zoo, several lakes, and a genuine castle on top of a hill.

Templo Mayor in the city center is an architectural site containing Aztec ruins. Tens of thousands pilgrimage to Basilica de Nuestra Senora de Guadalupe, which is the second-most-visited Catholic site in the world after the Vatican. If you have a day, take a tour about 90 minutes outside the city to the pyramids of Teotihuacan. When daytime sightseeing ends, nightlife kicks into high gear in the Zona Rosa—but look out for your money and your morals, as this translates to Red Light Zone.