This is an exception.  If you want to see what castles looked like in the Cathar period, pay a visit to the village of Pieusse, near Limoux.  Although you will find it in no tourist literature, this is the most representative "Cathar Castle" still standing.  

It is in private hands and not open to the public - which is why you won't find it in the tourist literature (no one to take your money).

It looks nothing like Carcassonne or the romantic castles of modern imagination, more like a giant vertically elongated shed, especially with its modern roof. It is in fact a keep or "donjon" - the structure on top of a "motte and bailey" defense familiar to many Europeans from their schooldays. It is a more complete version of the sort of château that you will find (in ruins) at Montaillou.

It was here that a famous Cathar Council (Concile Cathare) was held in 1225 and where the first and only Cathar bishop of the Razés was elected.His name was Benedict of Termes (Benôit de Termes), the brother of Raymond of Termes, the Lord of Termes. The council was held in a room in the château at Pieusse, but it is commemorated in the name of the "place" just outside.

Google map showing Le Chateau de Pieusse