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The Lee Navigation is a canalised river incorporating the River Lea (River Lee). It runs from Hertford Castle Weir to the River Thames at Bow Creek; its first lock is Hertford Lock and its last Bow Locks.
See Wikipedia article: Link

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