The Piccadilly line is a line of the London Underground, coloured dark blue on the Tube map. It is the fifth busiest line on the Underground network on the basis of the number of passengers transported per year. It is mainly a deep-level line, running from the north to the west of London via Zone 1, with a number of surface sections mostly in its westernmost parts. Out of the 53 stations served, 25 are underground. It is the second longest line on the system, after the Central Line. It serves many of London's top tourist attractions including Harrods, Hyde Park, Buckingham Palace, Piccadilly Circus (after which the line is named), Leicester Square and Covent Garden, as well as London's biggest airport, Heathrow.
http://en.wikipedia.org/wiki/Piccadilly_line
