Flat-as-a-griddle Treasure Island, built on the shoals of neighbouring Yerba Buena Island, is entirely man-made from boulders and sand. Originally constructed as a site for 1939's Golden Gate International Exposition, the island was seized by the US Navy in 1942. It served as a troop deployment staging area for many years, until it was returned to the city in 1997. At around this time it was determined that the entire island sinks a bit deeper into the Bay each year. Despite this, it now functions as a sort of mid-Bay suburb, with some lucky San Franciscans moving into the former military housing. Why lucky? The views are spectacular, as many Hollywood location scouts have realised: parts of The Caine Mutiny and two of the Indiana Jones movies were filmed here. In 2007, the island hosted the first Treasure Island Music Festival (treasureislandfestival.com). Yerba Buena Island - literally, 'Good Herb Island' (the Yerba Buena referred to is actually an aromatic perennial from the mint family used in medicinal tea by Native Americans) - is an important Coast Guard station. You can drive on the island's one road, but there's nowhere to stop.