The Old Ship Saloon on Pacific Avenue claims to be San Francisco's oldest bar, and the claim is hard to argue with -- it is literally built into the hull of a Gold Rush-era ship. The Arkansas sailed around Cape Horn in 1849, was beached in what was then the waterfront (now several blocks inland thanks to landfill), and became a drinking establishment when the crew left to seek their fortunes.
Today it is a handsome, unpretentious bar with good beers on tap and a strong sense of history. The Barbary Coast is long gone, but drinking here you can feel its echo. The area around Pacific and Battery was once the most dangerous waterfront in America.