Fotheringay Castle, Northants.

This castle, with its Mary Queen of Scots asociations, is probably the most romantic castle site in England,and a magnet for visitors. Too bad that it doesn’t exist any more; you can visit the castle mound, but all that visibly remains of the great castle is a tumbled chunk of masonry at the foot of the mound that might have come from its walls.
As a consolation prize, the village has many attractive buildings in honey coloured stone, and the great 15th Century Collegiate Church should be worth a visit. (I didn’t see it when I visited the “castle” as I knew nothing about it.)