Tubewalker: The Tube, On Foot

'In its simplest form, a tubewalk is nothing more than a walk that starts and ends at a Tube station, so all you need to become a tubewalker is a couple of Tube stations, a dose of motivation and some time to kill. You certainly don't need someone like me laying down rules. However, I did need some rules, because in summer 2008, I set myself the challenge of tubewalking the entire Tube network, and something that big needs a few rules. I therefore formulated the following guidelines for my own, personal tubewalk before I set off ...'