You are looking for a small magnetised cache at the top end of the park. There is room for logbook only, so BYOP. Tweezers will also be useful (or give it a good flick).
Parking is available on the road near the main entrance to the park.
Watch out for doggy muggles around here, and anyone appearing from the little side path.
Also, please be careful whilst retrieving as it could be difficult to recover if dropped.
*** FTF kudos goes to Toshack61 ***