The closest is Saarbrücken Castle, 1 km south-west of the city centre; the most famous is Porta Nigra (#88 of 9,040 worldwide) 64 km north-west. The oldest dated site in the circle is Celtic circular wall of Otzenhausen, founded c. 350 BC.
The 100 km circle reaches into 3 countries: Germany (60), France (50), Luxembourg (42).
