The closest is Citadel of Besançon, 1 km south-east of the city centre; the most famous is Palace of the Dukes of Burgundy (#751 of 9,035 worldwide) 74 km west. The oldest dated site in the circle is Neuchâtel Castle, founded c. 975.
The 100 km circle reaches into 2 countries: Switzerland (39), France (14).