Picture a rocky island surrounded by icy water and thick fog. That is Alcatraz, located in San Francisco Bay. For nearly 30 years, it served as a federal prison for dangerous criminals. Famous prisoners included Al Capone, a powerful gangster, and Robert Stroud, known as the Birdman of Alcatraz. The prison was considered escape-proof. The island sits over a mile from shore. The water temperature rarely rises above 55 degrees, and powerful currents pull swimmers toward the open ocean. Guards watched from tall towers day and night. Despite these obstacles, some prisoners tried to escape. In 1962, three men crawled through vents and paddled away on a raft made from raincoats. They were never found. On March 21, 1963, Alcatraz closed. The saltwater had damaged the buildings, and repairs were too expensive. The government decided it was cheaper to send prisoners elsewhere. Today, Alcatraz is part of the Golden Gate National Recreation Area. Over a million tourists visit each year.