Close to GZ there is an old and mostly overlooked stone boundary marker. It marks the boundary between the old City of Sheffield and the area then under the jurisdiction of Wortley Rural District Council.
Nowadays the only boundary here is between the S6 and S35 postcode areas. The current boundary between Sheffield and Barnsley is a mile or so further up the road, and just after this is the small village of Wortley itself.
It was in 1974 that Wortley RDC was split, Ecclesfield and Bradfield becoming part of the new Sheffield Metropolitan Borough (replacing the old Sheffield County Borough) while Wortley and Tankersley became part of Barnsley.
The cache here isn't intended to be too taxing to find. Please bring your own pen and, as ever, watch out for muggles. Happy finding!