The closest is Depedogen, 1 km south-west of the city centre; the most famous is Walls of Dubrovnik (#336 of 9,035 worldwide) 97 km west. The oldest dated site in the circle is Klobuk Fortress, founded c. 850.
The 100 km circle reaches into 4 countries: Montenegro (12), Croatia (6), Albania (5), Bosnia and Herzegovina (2).