The Financial District holds two cities a block apart: the glass-and-steel downtown built on filled-in bay, and the brick survivor of the 1906 fire that the towers grew up around. Walk one into the other.
Start in the Montgomery Street canyon, where the towers lean over the road. This was the waterfront once — every block east of here is reclaimed Gold Rush mud. North to the Transamerica Pyramid, the white spire that ran the skyline for half a century; round its east side is a grove of coast redwoods, open and shaded, on the block where Mark Twain once worked. Sit under the trees a while.
Then cross Columbus, and the towers simply end. Jackson Square is the oldest standing district in San Francisco, its low brick blocks saved in 1906 because the fire crews chose to save the whiskey warehouses. Antique dealers fill the old shopfronts now. Slip into Hotaling Place, a cobbled alley with the gas lamps still up, and read the plaque about the liquor that outlasted the flames. End on California Street and the cable car hauling up toward Nob Hill.