Highbury Fields

Islington's largest open space, which says more about Islington than about the fields: twenty-nine acres of plane trees and grass, and the only real green for some distance in any direction. Londoners camped here after the Great Fire in 1666, and in 1970 it held Britain's first gay rights demonstration. Busy at every hour anybody is awake.

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.