On Thursday I went by train to Carcassonne. Carcassonne is a major town with more than 40,000 inhabitants and the Departmental capital (of Aude), but the only bit of it that gets any tourist attention is the Cite. This is the old part of the city, which is enclosed by a completely intact (after 19th century repair) circuit of fortifications and which sits on a hill-top on the other side of the river (the Aude) from the "new" town (Ville Basse), which wasn't founded till 1247!
The Cite is definitely worth seeing. It includes a Romano-Gallic tower and stretches of wall from the same period, lots of 10th to 12th century walls and towers, and a huge mass of 13th century fortifications (built by the King of France, most of the walls weren't there in 1209 when the crusaders besieged it), with repairs (and some totally ahistorical pointy turrets) added by Viollet-le-Duc in the 19th century. There is also a basilica (St Nazaire) which is a bit of an awkward mix of Romanesque and Gothic, but has some lovely stained glass roses. Most of the other buildings are ok, if more modern, but the place is one giant tourist trap, full of restaurants, souvenir shops, and such-like. A bit off-putting after a while.
The Ville Basse is also worth a visit. It has some nice churches — the cathedral and several others date to the 13th century! — which don't get any mention whatsoever in the Lonely Planet guide or the books about Carcassonne.
The youth hostel is right in the middle of the Cite, which is rather convenient. My one night there didn't leave me with a great impression, though — there was a group of about fifty screaming 12 year olds staying there, and the guy in the bunk across the room from me had an awesomely loud snore which kept me awake. I have decided not to go for the youth hostels for my six days in Paris. Since they seem to cost about 120 FF ($30) a night anyway, cheap hotels aren't much more expensive (going by the guidebook, they can even be cheaper).
After returning to Toulouse on Friday, I visited Saint Sernin, the one major church in Toulouse I hadn't been into yet. (It's 'only' a basilica, but I think it's more impressive than the cathedral, Saint Etienne.) Here, instead of using red-brick on the outside and stone on the inside, they used them together (and more effectively than Saint-Etienne), so the inside has a pleasant warmth to it due to the bricks. It also has a pleasing simplicity and lack of ornamentation, and an unusual double-aisle construction. (Can someone tell me why the couple are always said to walk down the aisle at a wedding, when in fact they are walking down the nave?) It is apparently the biggest Romanesque structure in France, and though it's not as big as the larger gothic cathedrals, it has a perfection all of its own.