Access to the place
Hiking to the start 5'
Go down the Spanish side of the road and at the bottom of the 1st large bend to the left, fork right onto the wide signposted path (piste in summer). The Col de Bargège is visible from the pass and the route is obvious.
The hike has a northerly exposure under the trees up to the pass, then a southerly and south-westerly exposure thereafter, so it's sunny.
Col de Barège
Follow the large laces of the track that climbs up very gradually, or cut off (after a large rock on the right, marked white/yellow path) to avoid the very large final lace. Once out of the forest, you're below the pass. All you have to do then is climb the open section leading to the wide goulet and the small refuge. Magnificent views of the Luchonnais and the Aneto massif.
Tuc du Plan de la Serre
This is the summit on the right as you look towards Luchon (i.e. north-west). Yaw up the first visible summit (steeper) and then follow the rounded ridge for a few hundred metres to reach the summit. A balcony overlooking the region, with views of Super-Bagnère, the central Pyrenees and the valley from Saint Béat to Luchon.
This is the downside of the hike, since you have to make a round trip. But the descent is much quicker, cutting through the snow from the Tuc to the pass and then cutting all the switchbacks from the entrance to the forest to the Col du Portillon.