Its first section opened in 1863, and it was the first underground railway system in the world. According to UK wikipedia, there are 270 stations in London now. It is the longest metro system in the world and the third busiest metro system in Europe after Paris and Moscow.
Among many different pros and cons of London tube, I chose 3 general things for each. Due to dense rail network, we can have more than two ways to get to our destination easily. Also we don't have to wait for tube a long time and there is wide range of payment system like oyster, travel card, pay as you go. In spite of this diversity, it is hard to put up with its high fares. When I got on London tube for the first time, I was so surprised its size and the fact we always have to check if the station is closed or not. I think small size causes not only inconvenience but also overcrowding in tube.
Because I was wondering why I couldn't use mobile in tube, I found the reason. At first, people were not able to use mobiles in tube because GSM which is a frequency way of the UK couldn't go through underground. Nowadays British people are opposed to speak over the phone in tube even though they have enough technology to make a call below ground. Unbearable noise from the tube and mp3 players already surrounds people, so they are anxious about another noise from mobile phone. It was interesting for me because before I knew this fact, I had thought 'Poor Londoners can't experience high technology'. It was my misunderstanding!
While other countries use the word 'subway', only the UK call it 'tube'. The term 'tube' came from the shape of round tunnel. Most Londoners don't sleep but read book or newspapers in tube. It is very different aspect comparing with Korea. About half of Koreans sleep and the rest of them usually watch videos or spend time with their mobile phones in subway. The most interest thing is London tube tends to be regarded as one of the cleanest and most convenient among the Europe's underground. Frankly speaking, it is terrible considering all over the world.
London commuters' monthly tube fare is more than twice of New York,Paris, or Rome. Besides, we can't get the transfer discount. Different fares apply to the time and it also depends on the zones. That's why you'd better use oyster card. Here is the fare for oyster & student oyster card.
You can get more information about transport for London and oyster card in here : http://www.tfl.gov.uk/
London underground song : http://www.youtube.com/watch?v=BgwoPG63B3Y