The London Underground is a metro system serving a large part of Greater London and neighbouring areas of Essex, Hertfordshire and Buckinghamshire in England. It is the world's oldest underground railway system. It is usually referred to as the Underground or the Tube - the latter deriving from the shape of the system's deep-bore tunnels - although about 55% of the network is above ground.
Read more about The Tube at
Wikipedia and there's even a Wiki page with information about
Mind The Gap :)
