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The Grand Union is a 137 mile (220km), 166 lock, 2 tunnel canal running between Brentford in London and Birmingham. It is the longest canal in Britain, and has 11 main arms and junctions. It takes over a week to navigate.

The Leicester arm branches off at Norton Junction and runs 66 miles long through 59 locks (including 2 staircase locks at Foxton) and 2 tunnels to Leicester where it continues into the River Soar.

Read more at Wikipedia Link

The River Brent rises in Barnet and flows southwards to meet the River Thames at Brentford, a distance of 17 miles. The lower part of the river, from Hanwell is part of the Grand Union Canal.
Wikipedia: Link

A 145 mile walk following the Grand Union Canal. This first national waterways walk was created as part of the celebrations of the 200th anniversary of the creation of the canal companies that later formed the Grand Union Canal. Being almost entirely towpath it provides much for those interested in canal history.
From the centre of London at Little Venice the canal heads to Slough and then through Hertfordshire and the Chilterns to Tring. Apart from the stretch through Milton Keynes the route is then largely rural passing the Canal Museum at Stoke Bruerne to Leamington Spa and Warwick. The final stretch is through the suburbs of Birmingham. Logo, see TQ1678 : Three walk logos, Gallows Bridge

The Capital Ring is a surprisingly green route that encircles London. Distance is 78miles; it threads together parks and open spaces, mostly following pleasant residential roads in between. The route is an initiative of the London Walking Forum. The route is very well signed, with a Big Ben logo TQ1678 : Three walk logos, Gallows Bridge. The route is a walker’s equivalent of the North and South Circular roads. Link