Geoff Marshall - Riding The Tideway Tunnel Train, 05122019

Under London, 45 metres below ground level, London is building a new super sewer system running alongside the River Thames to help keep it clean - and to help build the sewer there are several trains running deeper than tube lines down below

TED Ed (Animation) - How the world's first metro system was built, 19042018

It was the dawn of 1863, and London's not-yet-opened subway system — the first of its kind in the world — had the city in an uproar. Most people thought the project, which cost more than 100 million dollars in today's money, would never work. So how did they do it? Christian Wolmar explains how the London Underground was built at a time when no one had built a railway under a city before.