There's no shortage of Diego Rivera murals in CDMX, but the Secretariat of Public Education was my favorite. Covering all of the walls of these two courtyards are 235 panels of murals done between 1923 and 1928. This was Rivera’s first major large-scale mural project. The themes center around workers, and the glorification of all things Mexican, especially the Mexican Revolution. Rivera named the two courtyards “Labor Courtyard” and the other the “Fiesta Courtyard” based on the themes he painted in each.
Entrance is free, you just have to figure out where to go and get past some armed guards. I don't know the hours, but I went on a Monday afternoon, which was perfect since most all of the museums in Mexico City are closed on Mondays.
Murales de Diego Rivera en la Secretaria de Educacion Publica, Calle Republica de Argentina 28, Mexico City 06000, Mexico