In the middle ages there was much religious dissent and consequently many religious (as well as territorial) wars, which resulted in the construction of fortifications and remote monasteries. The Languedoc region was a Cathar stronghold, until they fell to the Albigensian crusaders, and there are still many historic sites which may be visited. The Cathar castles, Chateau d'Aguila, Chateau de Peyrepertuse, Chateau de Puilaurens, Chateau de Queribus and Chateau de Termes, which may be visited (some are free!) are known as the 5 sons of Carcassonne, and after the Cathars fell they were used to defend the border against the Spanish. Other Cathar castle remains within driving distance are at Montsegur, Rennes-le-Chateau, Chateau d'Arques and de Puivert. Rennes-le-Chateau and nearby Rennes-les-Bains, of course, have a more recent fame, or notoriety, due to the claims in the late 19th century of the priest Berenger Sauniere about the origins of treasure which appeared, and the Holy Grail. These mysteries were the basis of many bestselling books, and most recently underly the plot of Dan Brown's The Da Vinci Code. The history and mystery of this area also feature as the background or setting to other recent best-sellers: Sepulchre and Labyrinth by Kate Mosse and The Historian by Elizabeth Kostova.
Both the Prieure de Serrabone and the Abbeye de St Martin du Canigou are interesting old religious institutions set in spectacular mountain settings worth visiting. It is not possible to drive all the way to St Martin du Canigou: from the car park there is either a very steep 45 minute walk for the very fit, otherwise it is necessary to hire a jeep to complete the climb. Guided tours are available (and necessary) to visit inside the abbey.