This is Park Mount in Pulborough....on a dark night you might find the hidden treasure or witness another fairy funeral as one 18th century rector is reported to have done.
If you don't want to end up in trouble for trespassing might I suggest you don't undertake either of these activities as it's a scheduled monument on private land [the barbed wire fence rather gives it away]. It's a well preserved small 11th century Norman motte [the mound bit] and bailey [the courtyard area] castle. It may very well be that it's size is the very reason behind it having remained unaltered and abandoned in its original state. Despite some damage from quarrying this has made it one of the best surviving examples in the South East.
Much as I would have loved to have seen it closer up to this was the view from the public footpath.