Where It All Began
Mission Delores (1776) is the oldest building still standing in San Francisco, and was where the Catholic missionaries who founded the city for King Carlos III of Spain first settled. Depending on one's views, it is either a symbol of colonial oppression, Hispanic heritage, or the city's historical birthplace.
In any case, it is well worth a visit for the history, old altar, and the only cemetary left in the city center (all other graves were dug up and moved to Colma some time ago. To see the "Land of the Dead" for yourself, take BART to the Colma station to the south)