Built on Roman foundations from 1197, this mighty castle on the hilltop above Alken has an intriguing history. From 1246 to 1248 it was fought over by the archbishops of Cologne and Trier, and divided in two parts (separated by a wall). The peace agreement dated 17 September 1248 is one of the oldest surviving documents in the German language. Fascinating displays include medieval torture devices; the watchtower is accessible by ladder. Leaflets are available in English.
If you want to stay, there's a kitchen-equipped apartment (from €170) sleeping six people in a half-timbered wing, with a terrace overlooking the Moselle.