Barbury Castle is an Iron Age Hill Fort above Swindon. The Hill Fort has excellent views of the surrounding countryside (on a clear day you can see Uffington White Horse Hill).
Details of Barbury Castle are available on this web site and also this web site.
This Castle is on the Ridgeway footpath and has a car park with a picnic area, toilets, cafe and excellent views. It can get a bit bleak up here when there is a cold wind so remember a windproof coat. If you’re walking the Ridgeway then you’ll be really close to this one.
There is a choice of parking. The main car park is at N51°29.030', W01°46.640'. It is much the nicest place to park since it has excellent views and provides a nice walk over the hill fort to the cache. You could cache and dash at N51°29.167', W01°47.500'.
When you get to the posted coordinates (on the top of this page) then you'll find an information board. The first number in the text is the date that Barbury Castle was acquired by Wiltshire County Council. Call this ABCD.
The final cache is a short walk away at:
N51°29.D(B-C-D)D', W01°47.(C-D)DA.
The checksum for all the Northing coordinates is 21, and for the Westing is 20.
Please check out the Geocaching Association of Great Britain offering support for Geocachers in GB.