My folks are renting a house in the Ariege region, and I'm going to go and stay with them for a few days at the beginning of next month.
I'm flying into Carcassonne, and I'll have a free day there. Any tips?
Any ideas for good restaurants in the Ariege, particularly near St Girons?
Carcassone is a wonder, you will absolutely enjoy it. You could visit it seeing that you're landing there.
Concerning Carcassonne, you can easily spend the day in the old city, it's really a gem. For lunch you can try a cassoulet, which is one of the local specialty.
When you arrive in Ariege, pay a visit to the tourist board (office de tourisme), they should be able to provide you with a lot of information.
As for restaurants, you can ask around while there. I'm sure there are plenty of nice places.
Totally agree with what has been said previously on Carcassone.
Ariege is a very nice place for trekking. You should find plenty of information on this at the Tourist Office. You could visit the castles where Cathar heretics took refuge in the middle age before being exterminated by the king of France (Monsegur for instance).
If you like history and gastronomy, you could try "Lugdunum" restaurant near St Bertrand de Comminge, which specialises in antique roman cuisine (you will find their web site on google). It is not strictly speaking in Ariege but is fairly close from the place where you are planning to stay.
Have a nice time
Carcassonne is an amazing stop to make! The huge Medieval city is a big tourist attraction in Catalonian France. Make sure you bring your camera, and you should try to see it from a distance as well, I think it's most impressive when you can see it all at a glance. Also beware buying most things (souvenirs, snacks and meals) can be a little pricey in the actual site. Enjoy!