If you're caught you will get sent to D-Block solitary, a tiny cube where days are marked by a light shaft travelling across the wall - or you might be interrogated using techniques only alluded to in the otherwise thorough Alcatraz audio tour, with first-hand accounts by prison guards and prisoners of the Rock.

BBC: A tour of San Francisco��s Alcatraz

He also plans to transform the 28m-long ventilation shaft into a subterranean climbing wall.

BBC: Reawakening the Underground

If we managed to dig a several hundred foot vertical shaft and the soil was feeling generous, not collapsing inward and waiting for us to build the wall, the challenge of casting this concrete would still be great.

FORBES: Why Can't We Start Building The World's Deepest Building?