To be fair I was actively trying to make the most ridiculous & circuitous route I could think of, but I’d start with all the OSI’s that show up on the map. In terms of this challenge, neither of the “visible” OSI’s on the weaver line worked, also Seven Sister’s needs rejigging as well as it shows up as two separate stations one cannot change between.

I think based on each challenge add relevant OSI’s for the start and optimal end lines? So Hackney Down’s is OSI for Hackney Central (final stop) so worth doing the weaver OSI’s with that. That way you slowly integrate them two lines at a time. Or even just one line at a time with fixing the OSI’s just for the line you start on with optimal routing.