The
Piccadilly line is a line of the
London Underground, coloured dark blue on the
Tube map. It is the fourth busiest line on the Underground network on the basis of the number of passengers transported per year with 210,000,000. 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. Of the 53 stations served, 25 are below ground. Some of its stations are shared with the
District line and some are shared with the
Metropolitan line. It is the second longest line on the system, after the
Central line, and has the second most stations, after the District line. It serves many of London's top tourist attractions including
Harrods (Knightsbridge),
Hyde Park,
Buckingham Palace (within walking distance from Green Park),
Piccadilly Circus (after which the line is named),
Leicester Square and
Covent Garden, as well as
London Heathrow Airport, the busiest airport in Europe (based on passenger numbers).