A superb race track of a road, just keeps going all the way to (or from) the visitor centre under the Millau Bridge across to Albi. Easy to get carried away, speeds can get very silly because its such a fast open road. Change to the D992 for the Millau bridge visitor centre near the Millau end.
This road takes you down the Tarn gorge going East from Millau, with its spectacular scenery and pretty twisty road along the gorge, and then cuts up a steep / difficult climb on a minor road (but with lots of hairpins) to Revens. From Revens it takes you into the Parc National de Cévennés along the D986 through more outrageously pretty scenery along well surfaced curves. Between Lesperou and Peyrolles the road is as good a fast mountain road as Ive come across, with tremendous curves, good road surface, not much traffic, and all the while pretty cool scenery. Remember to take the left turn at Valleraugue to get the good bits. Road numbering after Valleraugue is pretty random, but eventually at Saumane you pick up the D907 and find the curves near Peyrolles. Soon after Peyrolles the route goes left onto the D50 for the run into Alès, which while less dramatic than earlier remains a great curvey road to follow. Takes between 2 and 3 hours, and strongly recommend doing it in Summer.