Millfields Park #3: South Side
The cache, a small dark blue plastic bottle, is hidden towards the south-west corner of the Cricket Pitch part of Millfields Park. This is around 400m west of where the stadium described below was located.
***Please watch out for muggles as you undertake your caching activities and kindly replace the cache correctly concealed in its hidey hole - thanks!***
Millfields Park History (Part 3)
A stadium was built on the eastern side of South Millfields in the 1890s - originally called Whittles Athletic Ground it was mostly used for whippet racing. In 1896 Clapton Orient Football Club moved to the site from Pond Land Bridge, after which it became known as Millfields Road Stadium.
The football club began redeveloping the stadium, with large embankments built around the pitch using slag from the adjacent power station. In 1927 the Clapton Stadium Syndicate 
became joint tenants, and major alterations costing over £80,000 were made to the ground to allow for greyhound racing and the stadium became Clapton Stadium.
An oval track was installed around the football pitch, with covered concrete terracing laid on the three sides away from the main stand. The new layout was designed by Owen Williams, and the ground became London's 4th greyhound track, with its first meeting on 7 April 1928. In the same year the track hosted a new race over 400 yards that gained classic status called the Scurry Gold Cup. The football club got into financial trouble at the end of the 1920s and were forced to leave the ground, moving to the Lea Bridge Stadium.
In 1966 the Clapton Stadium shareholders contemplated a bid from the Greyhound Racing Association (GRA) which included two training sites with 180 acres and an interest in West Ham Stadium. The deal went ahead in 1967. In 1969 the track was then sold by GRA to redevelopers and the track's demise caused much upset. It eventually closed for the final time on 1 January 1974 and the Millfields Park Estate built in its place. See here, here and here for more detailed information and photos of the stadium.
The area south is the site of the coal-fired Millfields power station, now disused except as a sub-station. This was built in 1901, well before the creation of the National Grid in 1938, a period when power had to be generated near to the consumer. Coal was originally shipped up the Navigation from the Thames and it provided electric street lighting throughout the then Metropolitan Borough of Hackney. The focus in recent years has been on improving the infrastructure of the park and a Masterplan (see here for link) was commissioned in 2010 to help bring a strategic vision for the site.
Biodiversity improvements have also been implemented throughout the park following the LWT Management Plan report commissioned in 2010. The Millfields Users Group (MUG) work closely with the Parks Department and have secured funding for small projects in the park and sit on the Steering Group to deliver the Millfields Improvement plan.
(Information taken from Millfields Management Plan 2015-2020 p18)