The Kaiserpfalz — the imperial palace of Frederick Barbarossa — is the reason Kaiserslautern exists. Built in the twelfth century as one of the emperor's primary residences in western Germany, it sat at the edge of the great Palatinate Forest where Barbarossa and his court hunted. The palace was heavily used in the twelfth and thirteenth centuries, fell into ruin by the fifteenth, and was largely forgotten until nineteenth-century excavations revealed its extent.
The ruins are now being actively excavated and interpreted in the city centre, and visitors can walk around the exposed foundations and study the reconstructed plans. There is not a great deal to see in physical terms — this is archaeology, not architecture — but the scale of the original complex becomes apparent, and the setting, within a short walk of the modern town centre, is more atmospheric than most such sites.