London: buy a 1 day pass for the tube cause it's much cheaper!

Well, it depends on what zones you want to travel to (there are 6 zones in london). but i think that most tourists only need zone 1 and 2 so a pass would cost you 4.10 pounds. For this money you get to travel unlimitedly on all public transport, not only the tube (this includes buses and DLR) But there are some restrictions to it: you can't use it before 9.30 am or on night buses!