From London National Park City Wiki

Parkrun (stylised as parkrun) is a weekly timed run that takes place in participating parks all over the world. It was started 15 years ago by Paul Sinton-Hewitt and went from a small group of people in Bushy Park to something that over 350,000 people all over the world do every weekend. There are 1075 Parkrun events in the UK and 56 in Greater London. The runs take place in parks and local green spaces, in some areas including castles and beaches.

The route, which is 5km for adults and 2km for youth participants, can be completed by running, jogging, or walking; you can run with a dog on a leash, a guide runner if you are visually impaired, or a child under 11. You can also act as a volunteer, taking photos, marshalling, or directing (checking safety & announcing the welcome and rules). People find a community through volunteering even if they do not run, as Parkrun relies entirely upon volunteers to maintain safety standards and organisation.

There are no fees or entry requirements, and everyone is welcome to join. A one-time registration gives you a number that is scanned at the finish line to determine your time.