Similar to the DLR challenge, but to visit all the stations on the Southeastern train line that are inside the oyster zone. These aren't included on the standard tube map but on the National Rail 'Oyster Pay As You Go' map. I believe theres 71 of them, starting with the big ones like Charing Cross, London Bridge and Victoria. I guess you could do the same for the other mainline operators that have a large number of stations in London, such as First Capital Connect, Southern, South West Trains and Greater Anglia.
Thanks
