"When Hernan Cortés and his army of Spanish conquistadores arrived in México city—then Tenochtitlan—they raised the Aztec capital, destroyed its temples, and used many of the building materials to erect their own palaces and, famously, the Cathedral. There are few remnants left of what was once the capital of the vast Mesoamerican Empire, but the ruins of their most important temple, the Templo Mayor, which is located right next to the Zócalo, were discovered in the late '70s and have been open to visitors ever since. The site is an active archaeological dig, with some pretty impressive ancient frescoes, and an on-site museum displaying the thousands of ancient artefacts—elaborate offerings made for the gods—discovered here over the years."
