The closest is Palace of the Dukes of Lorraine, 1 km north-west of the city centre; the most famous is Château du Haut-Koenigsbourg (#226 of 9,035 worldwide) 99 km south-east. The oldest dated site in the circle is Titelberg, founded c. 100 BC.
The 100 km circle reaches into 3 countries: France (50), Luxembourg (9), Germany (2).