the tube. the underground is such an amazing system.. there are so many tunnels and lifts and steps and all the stations are sort of unique. they are quite expensive at the moment, as we are located in zone 3 which makes travelling to the city (zone 1) a bit pricey. we have just discovered weekly passes and can top up what is called an 'oyster card' with credit and use as much as you like in a week. all stations have electric scanners that automatically take the money off your card, and can also calculate the cheapest rate for you over a day period.