Underground, overground

This arrived in the post today; I’d seen an article about in last week’s Sunday paper and managed to get a copy which unexpectedly is signed by the author. Looking forward to doing some of the lines, probably starting with the Victoria line on my next visit.
It has also given me the idea to do similar with the subway in Glasgow - much more manageable at around 6 miles, plus some more for a less direct route above ground.