The tube is interesting. It's actually one of the first, if not the very first in the world. Get ready for clostrophobia if you have it. Tight spaces, rickety tracks and huge gaps/steps between the platforms, etc make for an adventure. Great city coverage though. Get an "oyster" card and use that. It's an RFID card that debits a prepaid amount for travel. You get discounts from the standard fares. Going all day? Even better, an all areas, all types (trains, bus, U, trams, etc) unlimited pass is 7.5GBP per person. DO NOT get that stupid tourist pass for 3 days. Total Rip off.

Very regular transport, I think it is one of the best underground systems that I have ever been on. However it can get busy very quickly! Avoid peak times (7:30 - 9:00 and 16:00 - 19:00). Always check online for travel on the weekends as there can be many rail improvement works, which means sections of the lines are closed. If in London for a long period of time invest in an Oyster card, the value of which can be redeemed when you return the card once finished, plus any unused 'top-up' credit. It's a lot more economical this way. Also remember, these stations are not that far apart so check and see that it might be worth walking a couple of stops instead of taking the tube. But on the whole I do highly recommend the tube.

The area really feels so congested especially during rush hours. I don't want to get in there during these hours. This is the subway I feel most uncomfortable with in my entire trip to Europe, small with lots of people I imagine it would be so difficult to get out in case of emergency.

Great way to get around in the city. Trains are fast, and running frequently. Stations seem to be quite safe (watch your bag as everywhere). Note which exit/entrance you take: some stations are big and you can get lost a little bit. ;-)

It`s the oldest metro in the world and if you wander around the stations you can find real gems but at the same time it`s in one of the biggest cities in the world so avoid it between 8 and 10 am and 4 and 6pm:)