London

London is the capital and largest city of England and the United Kingdom. Standing on the River Thames in the south-east of England, at the head of its 50-mile (80 km) estuary leading to the North Sea, London has been a major settlement for two millennia.

Londinium was founded by the Romans. The City of London, London's ancient core − an area of just 1.12 square miles (2.9 km2) and colloquially known as the Square Mile − retains boundaries that closely follow its medieval limits. The City of Westminster is also an Inner London borough holding city status. London is governed by the mayor of London and the London Assembly.

London has a diverse range of people and cultures, and more than 300 languages are spoken in the region. Its estimated mid-2018 municipal population (corresponding to Greater London) was 8,908,081, the third most populous of any city in Europe and accounts for 13.4% of the UK population.

London's urban area is the fourth most populous in Europe, after Moscow, Istanbul, and Paris, with 9,787,426 inhabitants at the 2011 census. The London commuter belt is the third-most populous in Europe, after the Moscow Metropolitan Area and Istanbul, with 14,040,163 inhabitants in 2016.

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 in Greenwich where the Royal Observatory, Greenwich defines the Prime Meridian (0° longitude) and Greenwich Mean Time.

Other landmarks include Buckingham Palace, the London Eye, Piccadilly Circus, St Paul's Cathedral, Tower Bridge, Trafalgar Square and The Shard. London has numerous museums, galleries, libraries and sporting events. These include the British Museum, National Gallery, Natural History Museum, Tate Modern, British Library and West End theatres. The London Underground is the oldest underground railway network in the world.

London is one of the leading tourist destinations in the world and in 2015 was ranked as the most visited city in the world with over 65 million visits. It is also the top city in the world by visitor cross-border spending, estimated at US$20.23 billion in 2015.

Tourism is one of London's prime industries, employing the equivalent of 350,000 full-time workers in 2003, and the city accounts for 54% of all inbound visitor spending in the UK.

In 2015 the top most-visited attractions in the UK were all in London. The top 10 most visited attractions were: (with visits per venue):

The British Museum: 6,820,686
The National Gallery: 5,908,254
The Natural History Museum (South Kensington): 5,284,023
The Southbank Centre: 5,102,883
Tate Modern: 4,712,581
The Victoria and Albert Museum (South Kensington): 3,432,325
The Science Museum: 3,356,212
Somerset House: 3,235,104
The Tower of London: 2,785,249
The National Portrait Gallery: 2,145,486

The number of hotel rooms in London in 2015 stood at 138,769, and is expected to grow over the years.

A 2013 report by the City of London Corporation said that London is the "greenest city" in Europe with 35,000 acres of public parks, woodlands and gardens. The largest parks in the central area of London are three of the eight Royal Parks, namely Hyde Park and its neighbour Kensington Gardens in the west, and Regent's Park to the north.

Hyde Park in particular is popular for sports and sometimes hosts open-air concerts. Regent's Park contains London Zoo, the world's oldest scientific zoo, and is near Madame Tussauds Wax Museum. Primrose Hill, immediately to the north of Regent's Park, at 256 feet (78 m) is a popular spot from which to view the city skyline.

Close to Hyde Park are smaller Royal Parks, Green Park and St. James's Park. A number of large parks lie outside the city centre, including Hampstead Heath and the remaining Royal Parks of Greenwich Park to the southeast and Bushy Park and Richmond Park (the largest) to the southwest, Hampton Court Park is also a royal park, but, because it contains a palace, it is administered by the Historic Royal Palaces, unlike the eight Royal Parks.

Close to Richmond Park is Kew Gardens which has the world's largest collection of living plants. In 2003, the gardens were put on the UNESCO list of World Heritage Sites. There are also parks administered by London's borough Councils, including Victoria Park in the East End and Battersea Park in the centre.

Some more informal, semi-natural open spaces also exist, including the 320-hectare (790-acre) Hampstead Heath of North London, and Epping Forest, which covers 2,476 hectares (6,118 acres) in the east. Both are controlled by the City of London Corporation.

Hampstead Heath incorporates Kenwood House, a former stately home and a popular location in the summer months when classical musical concerts are held by the lake, attracting thousands of people every weekend to enjoy the music, scenery and fireworks.

Epping Forest is a popular venue for various outdoor activities, including mountain biking, walking, horse riding, golf, angling, and orienteering.

London is a major international air transport hub with the busiest city airspace in the world. Eight airports use the word London in their name, but most traffic passes through six of these. Additionally, various other airports also serve London, catering primarily to general aviation flights.

London Heathrow Airport, in Hillingdon, West London, was for many years the busiest airport in the world for international traffic, and is the major hub of the nation's flag carrier, British Airways. In March 2008 its fifth terminal was opened. In 2014, Dubai gained from Heathrow the leading position in terms of international passenger traffic.

London Gatwick Airport, south of London in West Sussex, handles flights to more destinations than any other UK airport and is the main base of easyJet, the UK's largest airline by number of passengers.

London Stansted Airport, north-east of London in Essex, has flights that serve the greatest number of European destinations of any UK airport and is the main base of Ryanair, the world's largest international airline by number of international passengers.

London Luton Airport, to the north of London in Bedfordshire, is used by several budget airlines for short-haul flights.

London City Airport, the most central airport and the one with the shortest runway, in Newham, East London, is focused on business travellers, with a mixture of full-service short-haul scheduled flights and considerable business jet traffic.

London Southend Airport, east of London in Essex, is a smaller, regional airport that caters for short-haul flights on a limited, though growing, number of airlines. In 2017, international passengers made up over 95% of the total at Southend, the highest proportion of any London airport.

The London Underground, commonly referred to as the Tube, is the oldest and third longest metro system in the world. The system serves 270 stations and was formed from several private companies, including the world's first underground electric line, the City and South London Railway. It dates from 1863. Over four million journeys are made every day on the Underground network, over 1 billion each year.

There are more than 360 railway stations in the London Travelcard Zones on an extensive above-ground suburban railway network. South London, particularly, has a high concentration of railways as it has fewer Underground lines. Most rail lines terminate around the centre of London, running into eighteen terminal stations, with the exception of the Thameslink trains connecting Bedford in the north and Brighton in the south via Luton and Gatwick airports.

London is the centre of the National Rail network, with 70 per cent of rail journeys starting or ending in London. Like suburban rail services, regional and inter-city trains depart from several termini around the city centre, linking London with the rest of Britain including Birmingham, Brighton, Bristol, Cambridge, Cardiff, Chester, Derby, Holyhead (for Dublin), Edinburgh, Exeter, Glasgow, Leeds, Liverpool, Nottingham, Manchester, Newcastle upon Tyne, Norwich, Reading, Sheffield, York.

Some international railway services to Continental Europe were operated during the 20th century as boat trains, such as the Admiraal de Ruijter to Amsterdam and the Night Ferry to Paris and Brussels. The opening of the Channel Tunnel in 1994 connected London directly to the continental rail network, allowing Eurostar services to begin.

Since 2007, high-speed trains link St. Pancras International with Lille, Calais, Paris, Disneyland Paris, Brussels, Amsterdam and other European tourist destinations via the High Speed 1 rail link and the Channel Tunnel.

The first high-speed domestic trains started in June 2009 linking Kent to London. There are plans for a second high speed line linking London to the Midlands, North West England, and Yorkshire.