Perched on some precipitous cliffs, the 11th- to 14th-century Forteresse de Mornas, 12km north of Orange, makes a dramatic backdrop for the pretty village below. Built by the medieval Counts of Toulouse, it commands outstanding views west to the Rhône and east to Mont Ventoux.
You can visit by yourself, or take one of the five guided tours (adult/child €9/7) available daily in July and August, or on weekends from April to June and in September.