Launched in June 1943, the S.S. Jeremiah O'Brien is the last surviving and still-operable example of the more than 2,700 Liberty ships churned out during World War II, and is a National Historic Landmark. After participating in the Normandy landings (she arrived on the French coast a few days after D-Day), the O'Brien was shifted to the Pacific for the duration of the war, with San Francisco as her home port. She's been a proud, if somewhat overlooked, fixture of the city's waterfront since being restored and opened to the public in 1980. Visitors are free to roam the ship on their own, including the labyrinthine engine room, with its countless pipes and stairways. And to think the ship was built in just 56 days! Open daily 10 a.m. to 4 p.m. Adults $7, kids 6-14 $4, children under 6 free.