This is the Northern Outfall Sewer Embankment (NOSE) AKA The Greenway and also partly Q22 of the Quietway cycle routes. Designed by Jospeh Bazalgette as part of the great Victorian sewerage solution this 7km route was covered over and opened as a walkway in the early 1990s as part of a green strategy. A great pedestrian and cycle route connecting Hackney Wick to Beckton and connecting with other off road local routes such as the River Lea, the Channelsea Path, the Long Wall Path and many other pathways around Beckton and the Thames.
It is open 24 hours a day and there is low level lighting along most of the Greenway and green corridors along the side that are a host to lots of interesting wildlife that you may see along the way. The Greenway is often busy with cyclists commuting and school run pedestrian traffic.
It is currently not recommended by the police that you use this area on your own in the evening whilst using your mobile phone due to a number of crimes in the area. Come with a friend or plan your trip for earlier in the day.
This is a simple offset multi. The cache is not at the posted coordinates but is a very short walk away. At the posted coordinates, you will find yourself in front of some concrete structures. These fortifications were built in 1940 under the orders of General Ironside and form part of what was the Outer London Defence Ring. Not so well known as London's City Wall or the Tower of London or the City Gates but nonetheless, their purpose was to protect London from invasion. This time, the threat was from the Nazis. The defence rings used a mixture of man made ditches and natural waterways, the River Lee forming a natural barrier and the steep embankments of the Greenway also. The pillbox would have housed machine gunners, the concrete barriers with holes in them would have been able to take steel beams, possibly railway lines to provide an anti tank barrier. The defences never saw enemy action.
From the posted coordinates:
count the total number of windows in the pill box for A (it's symmetrical)
count the number of holes in one of the tank defences for B
A few metres East along the Greenway there is a sign post (see waypoint) with two numbers on it for C.D
N51 32.(A-D)(B+D)A W000 01.(B-C)D(A-B)
You can check your answers for this puzzle on GeoChecker.com.