Thought to be of Celtic origins, this enormous red-sandstone hilltop castle was first documented in 1081. Between 1125 and 1298 it was the repository of imperial treasures including, allegedly, a nail from Jesus' cross and a tooth from John the Baptist. Richard the Lionheart (Richard I of England) was imprisoned here from 1193 to 1194 for insulting Leopold V, Duke of Austria. Today, the castle's displays include a replica of the imperial crown jewels.
Recent excavations have uncovered the remains of a wooden castle believed to date from Saxon times. One-hour guided tours (adult/child €10/7) in English take place at 3pm on Saturdays from May to October.