Dig Your Own Hole

"Using this technique, the team has made a remarkable discovery: they have found the remains of a military fortress, which was thought to have been destroyed.
"Standing in the middle of the yard, which is still enclosed by 6m-high (20ft) walls, Prof Everett points to a spot where he has found evidence of a subterranean tunnel system.
"'(The tunnels) would have been used for the fortifications. There would have been movement of man and ammunition; it would have been bomb proof and covered with earth so it would have been protected,' he explains.
"'We get signatures that indicate there is not only a tunnel, but magazine buildings too.'"


Rebecca Morelle at BBC.com explores "a hidden history lying beneath the prison of Alcatraz."