Dirty Great Machines

Last Episode, 18 May 2012: Season 1, Episode 4: Episode 4

In Canada, almost two miles underground in the world's deepest copper and zinc mine, a mighty drill chews through rock, digging deep holes which are then filled with explosives and detonated, leaving behind debris packed with valuable minerals. Meanwhile in Helsinki, Finland, cameras follow a mission to excavate a new metro tunnel to improve commuter services - but working seven metres beneath the bustling city calls for precision engineering and one false move could lead to disaster.