The capital and largest city of Mexico Ciudad de Mexico or Mexico City is a sprawling and crowded metropolis (it has about 20 million inhabitants) lying in a really high altitude of about 2 200 meters above sea level. You need about a week for detailed exploration, but if you want to see only the greatest sights, about 2 days can do well. The historic center called zócalo or Plaza de la Constitución is located in a place where was once the center of Tenochtitlan (the capital of the Aztec Empire), i.e. on the dried lake Texcoco. The center is today afflicted by its sinking, which is most evident in its dominant – the Cathedral.