Union Square is one of San Francisco's oldest public spaces, with the strangest of foundations: you are, quite literally, standing on the roof of a car park. The underground garage was added in the 1940s, one of the earlier urban reinventions of its kind.

The square gets its name from pro-Union Army rallies held here before the Civil War. At its centre stands the Dewey Monument, dedicated by President Teddy Roosevelt in 1903. The model for the statue, Alma de Bretteville, made ends meet as an artist's model before marrying Adolph Spreckels, the sugar baron. She coined the term "sugar daddy" and went on to found the Palace of the Legion of Honor.

VoiceMap's audio tours trace Union Square's Civil War history, connect Alma's story to San Francisco's art world, and follow the Hotel St. Francis from the 1906 earthquake to a presidential assassination attempt on its steps.