The best way to discover a city is on foot (at least if you ask me), and if that city happens to be London, you cannot skip the Regent's Canal Walk. The 15k path runs along the Regent's Canal all the way from Little Venice to the Thames River bank. En route, you'll encounter many quirky house boats, city parks, local joggers, cozy coffee shops and a few iconic landmarks like the London Zoo, Camden Lock, the 'Word on the Water' book barge and Gasholder Park.
If you're there on a Sunday and don't feel like doing the full walk, I recommend starting in Angel (Islington) and ending in Victoria Park with its Sunday market (every Sunday 10am-4pm).