The Valkhofpark ("Falcon's Court Park") is located on the site where until 1798 a castle stood, built by Charlemagne, destroyed by Vikings and rebuilt by emperor Frederick Barbarossa in 1155. After the French had destroyed much of the castle in 1795, and because the city needed money, the ruins of the castle in that year were sold and demolished for the stones. Only a chapel and the remnants of another remain.
The 16-sided St. Nicolaaskapel, originally a smaller copy of the chapel of Charlemagne's palace in Aachen, for a long time was thought to be one of the country's oldest buildings, dating from the late 8th century. It is now believed the chapel is less old, in fact not having been built before the 11th century. That still makes it one of the oldest buildings in the Netherlands. In the building's front are its oldest parts, but as can be clearly seen the chapel has had a few changes in both Romanesque and Gothic styles.
The remains of the choir of the castle's 12th-century church stand at the other side of the park. This Romanesque building was saved at the last moment, as a reminder. It's known as the Barbarossa ruin.