Located on Alcatraz Island in San Francisco Bay, the penitentiary was once home to gangsters and criminals including Al Capone, Alvin ‘Creepy’ Karpis, and George ‘Machine Gun’ Kelly.

Now, archaeologists have used ground-penetrating radar data and terrestrial laser scans to non-destructively uncover a hidden military traverse underneath the prison. Led by faculty at Binghamton University, State University of New York, the team also made use of georectifications – where old digitised maps are linked to a c
Source: NDT