Alcatraz, the notorious island prison surrounded by the waters of San Francisco Bay, is slowly giving up its secrets.
Researchers have now discovered extensive tunnels, embankments and other remnants of a military fortress hidden beneath the floors of the prison. Experts had thought these structures were completely destroyed long ago.
The fortress was discovered purely by accident, after concrete experts were called in to repair a small tripping hazard — a hole in the floor of the prison’s former recreation yard. When the experts took out a chunk of concrete, it exposed the top of an old battery wall from the 19th century. Read more.