London is a popular centre for tourism, one of its prime industries, employing the equivalent of 350,000 full-time workers in 2003, while annual expenditure by tourists is around £15 billion.London attracts over 14 million international visitors per year, making it Europe’s most visited city. London attracts 27 million overnight-stay visitors every year.
London contains four World Heritage Sites: the Tower of London; Kew Gardens; the site comprising the Palace of Westminster, Westminster Abbey, and St Margaret’s Church; and the historic settlement of Greenwich (in which the Royal Observatory marks the Prime Meridian, 0° longitude, and GMT).
Other famous landmarks include Buckingham Palace, the London Eye, Piccadilly Circus, St Paul’s Cathedral, Tower Bridge, Trafalgar Square, and The Shard. London is home to numerous museums, galleries, libraries, sporting events and other cultural institutions, including the British Museum, National Gallery, Tate Modern, British Library and 40 West End theatres.
The London Underground is the oldest underground railway network in the world.