The Circle line is a London Underground service that forms a spiral from Hammersmith to Edgware Road and then a loop around central London. The railway is underground in the central section and the loop east of Paddingdon, and unlike London’s deep level tube railways, the railway tunnels are just below the surface and of similar size to those on British main lines. Coloured yellow on the tube map, the 17-mile line serves 36 stations, including most of London’s main line railway termini.
