Cathars and Catharism in the Languedoc:   Cathar Castles:

First the bad news.  There is very little remaining from Cathar times, castles or anything else.  All of the main "Cathar Castles" advertised to tourists as romantic vestiges of the Cathar period are no such thing.  They are generally castles built by the French after the Cathar Crusade, and used to defend their new border with Aragon.  These castles were slighted, or left to decay, after the Treaty of the Pyrenees in the seventeenth century.  The justification for the deceit is that they are often built on the site of earlier castles occupied by vassals and allies of the Counts of Toulouse during the Cathar period. 

Broadly there are five categories of "Cathar Castle".

Genuine Cathar Castles, advertised as Cathar Castles:  There are very few of these, although you may find a few vestiges near to existing structures (eg castles at Peyrepertuse, and Puivert).  Carcassonne probably has the best claim to be a Cathar Castle, followed by three quarters of Cabaret (Lastours). 

Later French Castles built on the site of Cathar strongholds, advertised as Cathar Castles:  Coustaussa,  Puilaurens,  Montségur,  Queribus,  Termes,  Aguila.

French Castles with no Cathar connections, but sometimes advertised as Cathar Castles: such as  Arques.

Cathar Castles not generally advertised as Cathar Castles although they are:  Pieusse,  Le Bézu,  Usson.

There are also castles of interest because of their links with events during the Cathar period, for example: Avignonet, where Cathar sympathisers helped some particularly unpleasant Inquisitors into their next incarnations. Villerouge Termenès, a castle belonging the the Archbishop of Narbonne, where the last known Cathar Parfait in the Languedoc was burned alive, and Montaillou, the home of Beatrice de Plannissols, a major character in the events following the arrest of a whole village by the Inquisition on suspicion of Cathar sympathies.