Bosque de Chapultepec

This is a bit more than your average city park, the forest here is ancient, ancient, and it's been a sacred place for both the Aztec and Mexican people who've lived on this spot. Artefacts dating to the 4th century have been found here, but it's not just the age of the artefacts that is impressive, it's also the variety. Add to that the size—this park is Mexico's largest, with several decent sized lakes as well as caves and forests. The building on the top of the hill is Chapultepec Castle, which houses the National Museum of History, and within the park's bounds, you will also find the Tamayo Contemporary Art Museum, Mexico's Natural History Museum, a zoo and the National Museum of Anthropology and History—which may well be one of the main reasons you're visiting Mexico City.