While we were in France on our holiday, we went to see some of the Cathar castles, as we were right in the heart of the Cathar country. You'll find plenty about this on www.cathares.org. We went to see the castle of Aguilar (from a bit of a distance as the road looked quite twisty and I chickened out) and the castle of Quéribus (up, close and personal, despite my fear of mountain roads - it wasn't as bad as I feared!).
Here is a picture of Aguilar:
And a picture of Quéribus: