The closest is Hohenecken Castle, 6 km south-west of the city centre; the most famous is Eltz Castle — #75 of 9,079 worldwide — 90 km north. 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 (139), France (30), Luxembourg (1).