And don't forget Thetford Castle. Thats norman, built on an iron age fort. The motte looks scarily familiar though!
http://www.themodernantiquarian.com/site/2096/thetford_castle.html
laughs.....see how spookily familiar the folklore section is too
And of course there is Bartlow barrows, spookily Silbury like as well....
http://www.themodernantiquarian.com/site/4603/bartlow_hills.html