You know those runs which you really don’t want to do, make yourself start and then really enjoy? This wasn’t one of them. But it’s another run I can write “Done” next to in my plan and it adds another Northern Line station to my collection, so I’ll take it.
North Downs Way 100
abradypus 
So how does the Northern Line challenge work? Do you get the tube to the station and then run home?
Essentially, yes. Tube stations that I have run to or from in the course of a run commute.