The closest is Arco de los Blancos, 1 km south-east of the city centre; the most famous is Reales Alcázares (#68 of 9,035 worldwide) 98 km north. The oldest dated site in the circle is Castle of Jimena de la Frontera, founded c. 750.
The 100 km circle reaches into 3 countries: Spain (42), Gibraltar (2), Morocco (1).