From 1873 to 1954 a steam railway ran from Finsbury Park to Alexandra Palace. It was well known for being one of London's least reliable train lines, mainly because of the steep gradient - the steam locomotives could not cope.
Owing to its meandering route and strong competition from local bus services, service ceased on this line shortly after the 2nd World War. There was a plan to electrify the line and run tube trains however in the 50's London lacked the funds for an engineering operation of this scale. Work was abandoned; the rails were torn out and the line became the Parkland Walk.
Today, the Parkland walk is one of London's loveliest walking routes. You can find the southern-most extent of the route between a set of tennis courts on the North side of Finsbury Park (The park, not the station of the same name.)
The walk is tree-lined. On a warm summers day, it is easy to forget that this 'countryside path' is really cutting through some of London's most densely populated towns.
From Finsbury Park you can walk directly to Highgate tube station on the Northern Line. From there it is not possible to continue as a locked tunnel blocks your path. The far side of the tunnel is protected by a wire fence - it's actually the long abandoned platform of Highgate overground. If you ever get the chance, it's worth scrambling through one of the holes in the fence to see - an eerily disused platform with 50 years worth of trees growing through it!
After a short detour you can re-join the Parkland Walk, 500 metres to the West, and then stay on the path to enjoy the fabulous view of the whole of London from an enormous nine-arch railway bridge.
Your journey ends a kilometre later at the top of Alexandra Palace hill. A health club now stands on the site where the final railway platform would be. The old railway building is now a creche. This is a great place to stop and enjoy the view - There is a pub next door to the BBC transmitter at the top of the hill.