Clapham Common

Two hundred-odd acres of flat open grass with very little landscaping, which turns out to be exactly what most dogs want. It is one of the most dog-populated spaces in London on a Sunday morning, so a dog who is good with other dogs will have a lovely time, and one who is not will have a long one.

Hapoo counts the walk you were doing anyway

Read off your phone's motion sensor after the fact, so there is no start button and nothing running in your pocket. Characters turn up at real park gates across London, this one included.