Mexico City, Mexico - La Catedral de Guadalupe. Always filled with the faithful and travellers, this church is located in the center of the city. By the way, this church was erected by Montezuma over an Aztec temple. Most of the Capital is built directly over the ancient Aztec City called Tenochtitlan.
How on earth would you feed a city of over 200,000 people when the land around you was a swampy lake? Seems like an impossible task, but the Aztec managed it by creating floating gardens known as chinampas, then they farmed them intensively.