159 “Ground-Penetrating Radar Reveals Military Structures Buried Beneath Alcatraz Penitentiary Using non-invasive techniques, archaeologists have confirmed the presence of a coastal fortification beneath what was once the prison’s recreation yard. (twitter.com) posted 1 year ago by Joys1Daughter 1 year ago by Joys1Daughter +159 / -0 33 comments share 33 comments share save hide report block hide replies
This is old news to us long timers. Alcatraz was originally a military base and it's been well known there is an underground part / facilities ; possible more than one floor we were always told.