The cache is not at the headline coordinates. This is a bonus cache for those doing the Adventure Lab "Fowlmere Watercress Beds SSSI" which is a walk around RSPB Fowlmere.
Whilst completing the Adventure Lab, you will pick up information to complete the co-ordinates below and find this bonus cache as part of the walk.
Please note that this bonus cache is outside the reserve boundaries.
The cache is at N52 05.ABC E000 03.DEF.