Since the dawn of the 19th Century, rail networks have overcome almost all nature can throw at them. But there's one environment, which is their nemesis. Water. In this episode we discover how some of our greatest Railways have challenged engineering's greatest minds in their efforts to conquer our ‘water world's'. Whether bridging the notoriously swampy waters encountered in America's New Orleans, or tunnelling beneath the World's busiest shipping lane, the English Channel, or helping ships to navigate through the Panama Canal, each railway has solved a seemingly impossible problem, to create some of the most dramatic train journeys in the world.