I'm counting Weeton as the half-castle. Both because there isn't very much of it left, and because the "castle" part is a misnomer; it was only ever a manor house, not fortified; it does have a moat, but that was there purely for decoration / status.

I did enjoy Grimes Graves, although part of me thought that it was a lot of fuss about a hole in the ground. We went to the eco-centre; it wasn't really open, being a Saturday, but they did let us wander round.