Location of the final duel at the castle ruin

This castle is the chateau de Commarque. It's about 15 km to the Northwest of Sarlat in the Dordogne area of France.
The Keep and the Great Hall were the 2 locations used in the final duel.

http://www.best-of-perigord.tm.fr/sites/chateaux/commarque/chateauuk.html
http://www.pbase.com/steve_sharp/image/67029405
http://www.commarque.com

In 1994 excavation of the site was started because of other ruins on the site. The trees are being moved back from the ruins.

If you use Google Earth, search on 'Les Eyzies dordogne france' and to the North East there is a blue dot indicating a photo.

The Dordogne is now apparently heavily visited by English so it is much more touristy than it was 30 years ago. Sigh....

Late reply though, but it has been filmed at the Commarque ruin. (Chateaux de Commarque). I visited the ruins 2 weeks ago during my holidays in France. Most of the trees and vegetation covering the ruins, has been removed. Visit the site for more info: http://www.commarque.com/

In the director's commentary, Ridley Scott described how finding the castle was a complete surprise. They were trekking through the forests looking for a location for the final duel when they accidentally came upon the ruins of the castle and immediately knew they had to shoot the scene there. He also talked about how the sun accidentally came out during those final moments and that he let the movement of the sun dictate how he should direct the scene. Fascinating and wonderful commentary about the movie's production.