London Heathrow Airport — London, United Kingdom

Europe's busiest airport by passenger numbers, LHR grew from a small pre-war airfield west of London into the primary long-haul hub for British Airways and a cornerstone of the oneworld alliance, handling an extraordinary mix of transfer passengers connecting between continents. Its two parallel runways, unusually few given the airport's overall traffic volume, have made Heathrow one of the most intensively used runway pairs anywhere, and proposals for a third runway have generated decades of political, environmental, and legal argument without resolution. Terminal 5, opened in 2008 largely for British Airways operations, and the rebuilt Terminal 2, reopened in 2014, represent the airport's most recent major construction efforts, replacing older facilities dating to the mid-twentieth century. Heathrow anchors motorway links and the Piccadilly line and Elizabeth line rail connections into central London, reinforcing its role as Britain's principal gateway to the wider world.