London is the capital city of both England and the United Kingdom. It has a population of over 8 million people and is visited by nearly 26 million tourists each year. Some of London's most famous landmarks include Buckingham Palace, the Tower of London, Big Ben, St. Paul's Cathedral, Tower Bridge, Hyde Park, and Trafalgar Square. The city has an extensive public transportation system including the iconic red double-decker buses and black taxi cabs, as well as the world's oldest underground metro system known locally as the Tube.