Hackney Marshes is an area of grassland on the western (Middlesex) bank of the River Lee in the London Borough of Hackney. It was incorporated into the Lee Valley Park in 1967. It was originally a true marsh, but was extensively drained from Medieval times, and rubble was dumped here from buildings damaged by air raids during World War II.
Today the marshes provide many pleasant walks, in reach of the inner city, but the most famous use of Hackney Marshes is for Sunday league football, with 88 full-size football pitches marked out. On a typical Sunday, over 100 matches are played by amateur teams in several local leagues.
You can view a Bing map of the place here.