... and precious little else.
Which explains why I wasn't aware of it. It was built in 1116 and captured and destroyed shortly after. It's also on private land with no public footpath running anywhere near it.
However, I decided I had to go and see if I could get a photo. So today I sauntered casually along the lane running by the foot of the hill and checked out possible ways up. One track would have taken me in the right direction, but it was directly facing a cottage and anyone sneaking uphill would be in direct view of all the windows. I think I have found a route and the building shown on the map that you would have to pass to reach the castle site seems to be just a ruined barn.
So, an expedition to take photos is on the cards, preferably very early in the morning to minimise the chances of being spotted and told to bugger off. Our local farmers are not dairy farmers and thus don't tend to get up particularly early. With luck, they'll be lying in bed on a Sunday morning, which is probably the best day to attempt this.