Stoke Park is of considerable interest as the best documented and most complete surviving landscape design by Thomas Wright. Barn Wood contains the Beaufort Memorial (Wright 1756, listed grade II), the cold bath (Wright c 1750, listed grade II), a stone tunnel (Wright c 1750, listed grade II), and the surviving footings of the Rotunda (Wright 1755-6). Barn Wood contains the remains of a footpath system which gave access to the woodland gardens.
You're looking for a 35mm film canister.
The entrance to Stoke Park is easily accessed from Long Down Avenue and the geocache's location can be accessed through pre-existing paths.