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 ticketing Tamil, Turkish and Urdu. Prior to 2009, some ticket machines were multilingual; they supported six languages and those machines had English, Spanish, French, German, Italian, and Japanese. The new languages were added as part of the Investment Programme of LU. London Underground ticketing The London Underground metro system of London, England uses a mix of paper and electronic smart-card ticketing. London Underground uses Transport for London's Travelcard zones to calculate fares, including fares on the Underground only. Travelcard Zone 1 is the most central, with a boundary just outside the Circle line and Travelcard Zone 6 is the most outlying