There are three amazing murals by Diego Rivera in San Francisco. "Allegory of California" is at the The City Club (tours closed for now), "The Making of a Fresco Showing the Building of a City" is at the Art Institute, and now on display after being in storage for years is "Pan American Unity" at the SFMOMA.
It's awesome! 22 feet tall and 75 feet wide. It took me an hour just to look at it. It's masterfully populated with dozens of personalities important to Rivera as he hoped to influence American in joining the fight against fascism in WWII. Ancient Aztec goddesses are mirrored with Mussolini, Hitler and Stalin—and mocked by Charlie Chaplin.
You can see it for free.