In major cities around the world today, skyscrapers loom overhead, taxis sound their horns and street vendors peddle their wares. Below all of this lies city upon city, each with its fascinating and unknown history.

Washington DC is headquarters for one of the most powerful governments in the world, as well as some of the nation’s deepest secrets. The decisions made here echo around the world, so while the seat of power rests above these streets, the American nation’s security depends on what happens underneath them.

From top secret, high tech super-bunkers to the underbelly of Capitol Mall, we delve into DC’s subterranean defences. Host Don Wildman discovers how the US prepares for the worst, from the ravages of disease to nuclear catastrophe.