Norwich Castle Museum

You're standing at Norwich Castle, the fortress William the Conqueror had built here soon after he conquered England. Look up at that big square tower on the mound. That's the keep, about twenty-one metres high. It went up between 1094 and 1121, on an artificial hill that first carried a wooden castle. Thanks to those neat rows of blind arches on the outside, one nineteenth-century expert called it the most highly ornamented keep in England.