There is something in London, under Trasport for London called the Walk London that encompasses several tracks that are around various genres of interest like greenery, heritage, industrial history, Thames river bank, etc. One of it is called the Capital Ring that's the 78 mile walk through London's greenest suburbs. One section passes through Fryent Country Park & Brent Reservoir.
To Get There:
Nearest railway station: Wembley Park
Dedicated to Venkat