Montségur is in the Ariège département next door. It is famous for its castle, the last stronghold of the Cathars in 1244. In 1929, Otto Rahn was the first to link Montségur and the Cathars with the Holy Grail, hence its popularity. (Also see Rennes-le-Château.)
Roquefixade is a small town located between Lavelanet and Foix in the Ariège,
with the ruins of a 12th century castle on a cliff overlooking the village.
Foix is the capital of the Ariège. It is remarkable for its castle, built in the 7th century by the Counts of Foix. It is now a museum devoted to prehistory, Gallo-Roman and mediaeval archaeology. (website)