The Bakerloo line is a line of the London Underground, coloured brown on the Tube map. It runs partly on the surface and partly at deep level, from Elephant and Castle in Central London, via the West End, to Harrow & Wealdstone in the north-western outer suburbs. The line serves 25 stations, of which 15 are below ground. It is so called because it serves Baker Street and Waterloo. It is the ninth busiest line on the network, carrying over 111 million passengers annually.