Cathar Castles: The Cathars were Gnostic Christians. Their beliefs dated from the earliest Christian times but the Catholic Church regarded them as heretics. After a series of failed attempts to convert them, Pope Innocent III called a full scale massacre against them. The Cathars were burned alive by the hundreds. Their castles fell into the hands of the victors, and the area was annexed to France. Carcassonne and Lastours (Cabaret) have the best claims to be real Cathar Castles.
Puivert - south France : an original Cathar Castle not destructed during the crusade against the Albigensians by Louis IX, aka Saint Louis.