Airports of London cannot be expanded due to the docks on either side. It is also the only airport serving London which does not operate at night. A light rail service from London City Airport DLR station, which adjoins the terminal building of London City Airport, links it to the financial district of the City of London at Bank and Monument stations, which offer interchanges with London Underground. Located in the London Borough of Hillingdon, Heathrow is by far the largest of London's airports and considered the main gateway into the United Kingdom for non-European visitors. Heathrow has four terminals and two parallel
London Underground London Underground The London Underground (also known simply as the Underground, or by its nickname the Tube) is a public rapid transit system serving the capital city London and some parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire in the United Kingdom. The Underground has its origins in the Metropolitan Railway, the world's first underground railway. Opened in 1863, it is now part of the Circle, Hammersmith & City and Metropolitan lines; the first line to operate underground electric traction trains, the City & South London Railway in 1890, is now part of the Northern line. The network