The D393 from Trie-sur-Baïse to Galan winds for 18km through classic Hautes-Pyrénées countryside - rolling hills, covered in forest with the occasional flat stretch across the valley floors. One of our go-to routes when the mountains are snow covered. Some tight corners, but no hairpins and rarely much traffic, although be aware of logging lorries and mud in the forested sections.
One of the lesser known Cols of the central Pyrénées (to visitors, anyway) but very popular with locals, cyclists and walkers. After climbing up the wooded valley road you climb to higher open mountain roads, often narrow and with the slippery evidence of passing animals, however it is quite possible to do the entire route without passing another vehicle.
The villages on the south side are pretty and the route spits you out - or begins - on the road up to the Peyresourde from Luchon.
Equally good in either direction.