Start at the Zócalo, or Plaza de la Constitución. It's dominated by a pole bearing an enormous Mexican flag, and is crowded with tourists, locals, children playing, men eyeing women, peddlers, artists and musicians. You could spend hours here just people-watching.
Turn to the north and go into the Catedral Metropolitana, the largest church in Latin America. Constructed between 1585 and 1813, it consists of a variety if architectural styles and is noted for its elaborately carved Altar de los Reyes. The Zócalo is built on the site of the Aztec island city of Tenochtitlan on Lake Texcoco. Though the Spaniards drained and filled in the lake, buildings in the Zócalo district, most especially the Catedral, have been sinking into the earth for years, and the walls and ceiling of the Catedral are covered with scaffolds and supports.
Go back outside to the Zócalo and turn left into the Palacio Nacional. Various governmental offices are located here, including that of the President of Mexico, not to mention the Miguel Lerdo de Tejada Library. On the wall of the main staircase is a vast mosaic by Diego Rivera depicting the history of Mexico.
Turn north and go up Seminario Street to the remains of the Aztec Templo Mayor, a pyramid that was dedicated to Tlaloc, god of rain and water and Huitzilopochtli, god of war. After exploring the archaeological excavation site, check out the eight-room, five-level museum at the back of the grounds that is filled with Aztec artifacts.
Exit the Templo Mayor site onto Justo Sierra Street, cross over to the north side, and examine the Rivera, Orozco and Siquieros murals at the Antiguo Colegio de San Ildefonso. One block west, at Donceles 105, is the Templo de la Enseñanza, a narrow Baroque church with a gold altarpiece laden with statues of saints. South of this, at Donceles 99, is the Museo de la Caricatura, a cartoon museum that includes works by José Guadalupe Posada, the political cartoonist best known for his images of Dia de los Muertos skeletons.
