Foix (45mins drive/train from Ax): The historic regional capital is a wonderful place to wonder around and enjoy a leisurely lunch.  The powerful Counts of Foix had their ancestral home here in the 3 towered castle that towers above the city, until the late 13th century, when it became a garrison.  Today it is a museum with much of interest about the history and the pre-history of the Ariege.

Carcassonne (90mins drive): Famous for its incredible walled city (le cite), often pictured bathed in spotlights in the evening/night, Carcassonne is a popular tourist destination.  The cite itself was built on its current spot by the Gauls, Romans, Visigoths, Moors and Franks. In the 13th Century it became a Cathar stronghold, but suffered in the Crusades.  By the 18th century it was 'little more than a slum' but was saved from demolition by the enthusiasm and vision of one individual, Viollet le Duc who encouraged the restoration that was completed by 1910. Unfortunately now only the lower section of the Cite walls are original, the rest having been restored or added later.  Although the inside the walls of the Cite have been fully developed for tourists, with shops and cafe's and souvenirs readily available, it is definitely worth a visit.  Walking around the outside of the walls is particularly pleasant, with some stunning views. The 'new' town outside of the Cite is also worth an explore, and in fact offers its own share of shops and restaurants, often at less inflated prices.

In reality, Rennes le Chateau is a small village with only 111 inhabitants, that none the less, attracted over 100,000 visitors last year.  It lies in a scenic area known for its towering mountains, deep gorges, forests, caves and wild remote plateaus.  The village church, where in the early 19th century, the priest Bérenger Saunière supposedly discovered a fortune, is small and somewhat bizarre in its decoration, a fact which seems to add fuel to the stories of clues for hidden treasure being secreted in the building.  

The interest in the area has affected the village to the extent where entry to the church is scheduled to be only for the first 15 minutes of every hour.  The church is closely supervised to prevent re-occurrence of previous zealous treasure hunters who have attempted to dig for treasure in the church building itself!  

If you are interested in Cathar history and the various mysteries abounding this area, then it is a must visit.  If not, then I would suggest you focus on the wine tasting in the area as an alternative!