The closest is Helblinghaus, 1 km west of the city centre; the most famous is Neuschwanstein Castle — #8 of 8,133 worldwide — 58 km north-west. The oldest dated site in the circle is Sigmundskron Castle, founded 945.
The 100 km circle reaches into 4 countries — Italy (24), Austria (19), Germany (17), Switzerland (2).