There's plenty for history buffs big and small to explore aboard the Jeremiah O'Brien, a veteran of D-Day and the only original ship to sail under its own steam to the 50th anniversary of the Allied invasion at Normandy. From the faithfully restored engine room to the officers' bunk rooms, it's a fascinating bit of World War II arcana. It occasionally leaves dock for cruises, so be sure to call ahead. At Pier 43, between Hyde & Jefferson Streets, you'll also find a flotilla of turn-of-the-19th-century ships, including the three-mast, square-rigged Balclutha. The San Francisco Maritime Museum, closed for restoration until 2009, is nearby.