We have been several time over the past 10 years. Assuming you are coming on the Motorway A20 (or N20 which is parallel) head for Souillac J55(on A20) and take the D703, probably signed Sarlat and Bergerac. Souillac is a busy town and the sign is easily missed (or was when we were last there) take care. This is a slow road for towing but the best we have found so far. About 20Km along D703 STAY on D703 NOT D704 to Sarlat. This is probably signed Carsac/Beynac. Go through Montfort, shortly after D46 on right signed Sarlat turn left at the Chateau and follow signs for the site.
If you have any other questions about the site or area we will do our best to answer them.
Enjoy!