If you go to the castle at certain times in the summer they do some mock fighting, a jousting tournament, and even fire the trebuchet if you fancy some action shooting as well as crumbly building shooting.
Although it's getting dark by the time the jousting starts so you'd need a decent fast lens, or flash. It finishes about 9:30 to 10pm if I remember correctly so it's OK value for money then.
Actually inside the castle there are some well preserved (reinstated?) interiors, suits or armour etc as well.