The British train system has a curious little kink in it: there's a number of 'ghost trains.' What are these ghost trains? They're lines that run in the middle of the night, with obscure scheduling so that no one knows about them. If you happen to spot one and want to buy a ticket for them, the conductors will try to talk you out of it.
Why do they exist? Apparently closing down a rail line is a very costly and time-consuming process that's full of bureaucracy and protests. Instead of going through that, they just keep the lines running.
The phenomenon is so large and mysterious, that there are people who hunt these trains and wait for them taking photos. They call themselves 'Ghosties" who travel the land looking for these trains.
Check out more info on them at the source