In the UK, each service is given a train identification indicator or "headcode" (as they used to be displayed at the end of the train). The indicator is 4 characters, with the first character being a number that indicates the type of train. A "1" indicates this is an express passenger service, whilst a "2" indicates that this is a local or stopping train.
So the challenge is, how far North can you get in a day, if you only travel by "Twos".
Here's the rules:
+ you can start on the first train of the morning out of any station
+ you must travel only on trains with a "2" headcode
+ you must always leave the station you arrived at no other forms of transport are allowed, including walking between stations
I won't leave any more details here... you'll have to watch the video to see how I get on and where I go and on which trains.
As I say at the end, this was the best I've come up with, but I'm happy to hear from you if you think there's another route that can gain more lattitude than I managed.
finally, I have to add a huge thanks to @travelling_turtle , who's previous exploits have given me the inspiration to try my own challenge. I'm sure if he'd done it, it would have been called #Two24