Victoria line

The Victoria line is a London Underground line that runs between Brixton in south London and Walthamstow Central in the north-east, via the West End. It is coloured light blue on the Tube map and is one of just two lines to run entirely below ground, the other being the Waterloo & City line.
Constructed in the 1960s, it was the first entirely new Underground line in London for 50 years and was designed to relieve congestion on other lines, particularly the Piccadilly line and the Charing Cross branch of the Northern line. The first section, from Walthamstow Central to Highbury & Islington, opened in September 1968, with an extension to Warren Street following soon afterward. By March 1969 the line reached Victoria station, with the southern portion to Brixton opening in 1971. Finally, Pimlico station was added in 1972.

Wikipedia