The London Underground - also known popularly as The Tube - has trains that criss-cross London in the largest underground rail network anywhere in the world (it was also the first, the first section of the Metropolitan Line dates back to 1863). The Tube is an easy method of transport even for new visitors to London.
Tube maps (http://www.tfl.gov.uk/gettingaround/1106.aspx) are freely available from any station, most tourist offices and are prominently displayed throughout stations and in the back of most diaries.
The Tube is made up of 11 lines each bearing a traditional name and a standard colour on the Tube map. To plan your trip on The Tube work out first which station is closest to your starting point and which closest to your destination. You are able to change freely between lines at interchange stations (providing you stay within the zones shown on your ticket).
Use the Tube Map to determine which line(s) you will take. Since the Tube Map is well designed it is very easy to work out how to get between any two stations, and since each station is clearly signed and announced it is easy to work out when to get off your train.
Visitors should be aware, however, that the Tube map is actually a diagram and not a scaled map, making it misleading for determining the relative distance between stations as it makes central stations appear further apart and somewhat out of place. In central London, taking The Tube for just one stop can be a waste of time; Londoners joke about the tourists who use the Tube to travel between Leicester Square and Covent Garden stations. This is especially true since the walk from a tube station entrance to the platform at some central stations can be extensive. The Tube map also gives no information on London's extensive overground bus network and its orbital rail network.
Trains run from around 5:30AM to about 1AM. This mode of transport is usually the fastest way to get from one part of London to the another, the only problem being the relative expense, and the fact that it can get extremely crowded during rush hours (7:30AM-9:30AM and 4:30PM-7PM). On warm days take a bottle of water with you.
You can use the Oyster to pay, or you can also buy magnetically encoded paper tickets from the information counters or the self-service machinese. The smaller machines only take coins, while the larger touch-screen machines also take bills and credit/debit cards (note that they only accept cards with an embedded micro-chip, old-style cards with a magnetic stripe only cannot be used). Paper tickets are relatively expensive with a flat fare of 3GBP for up to 4 zones and 4GBP for up to 6-zones. However, most machines also issue day-tickets that are also valid on other methods of transport. Keep hold of your ticket for the whole journey, you'll need it to exit the station as well.
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