Ghosts of the Swamp Abandoned Engineering : Season 5 Episode 6

Including an exploration of forgotten relics from the defence of America's homeland, at Fort Jackson, USA, concealed by the banks of the Mississippi River; a concrete behemoth at Lorient Sub Base, on the coast of France, that proved invulnerable to enemy bombardment; and a ghostly ruin at Gwrych that is now home to a haunting presence.