The London Underground, usually referred to as the Tube, is Europe's largest metro subway system and also the world's oldest.

Inaugurated in 1863, today it has 268 stations and covers 405 km of rail tracks. It transports over 976 million people yearly.

The Underground serves a large part of Greater London and neighbouring areas of Essex, Hertfordshire and Buckinghamshire in England.

Image: A general view of the London Underground. | Photograph: Dan Kitwood/Getty Images.