| | The '''London Underground''' (often referred to as "The Tube") is London's [[Subway|underground railway system]]. Many lines in the outskirts are at or above ground level. | | The '''London Underground''' (often referred to as "The Tube") is London's [[Subway|underground railway system]]. Many lines in the outskirts are at or above ground level. |
| − | It is comprised of the Bakerloo, Central, Circle, District, Hammersmith & City, Jubilee, Metropolitan, Northern, Piccadilly, Victoria and Waterloo & City lines. | + | It is comprised of the Bakerloo, Central, Circle, District, Hammersmith & City, Jubilee, Metropolitan, Northern, Piccadilly (serves [[London Heathrow Airport|Heathrow Airport]]), Victoria and Waterloo & City lines. |