Secret Alcatraz Tunnels Found Underneath Prison Rec Yard Reveal 'Significance' Of Island's Military Past

Long before Alcatraz prison housed some of America's most notorious criminals, the San Francisco Bay island was the site of a Civil War-era military base whose walls and tunnels were buried and forgotten - until now. Using ground-penetrating radar, a team of scientists have found a labyrinth of secret, 19th century tunnels hidden underneath the old prison rec yard.