Start from the parking area of El Rigüelo, placed north of the spanish village of Aísa. To get there, the only thing you have to do is drive to Aísa and follow the road north for some six or seven kilometers more. Last time I was over there, it was quite a narrow place. Bear this in mind and try to be on the spot rather early, that way you should have no parking problems.
Start walking north from the parking area, by a good path that crosses a metal fence and goes through low bushes. In no longer than twenty to thirty minutes you shall reach the prairies of el Rigüelo. Our route keeps going north from this point, crossing the big rocky step we can see right in front of us.
Approach the rocky step gaining altitude by the grassy ridge placed on your right (eastern) side, ruling over the valleys of Napazal (left-west) and Rigüelo (right-east). You shall have to cross the rocky barrier by a clear notch placed on the left, evident from the grassy ridge.
Afterwards, you shall be entering the karstic area placed south of Aspe. It is a thalweg without any technical difficulties, marked by cairns leading you to the Brecha de Aísa. This is a mountain pass where the northern route coming from Candanchú also leads, and can be easily seen in front of you (just on the french-spanish border). It shall be only question of reaching it and after that turning right (east) towards the summit. Just follow the ridge (or a little lower than that) to the western foresummit and scramble for the final meters' climb to get to the real one.
Another possibility is to reach the breach between the summit and that "western foresummit" by the southwest couloir, turning right just after entering the karstic area. Following this couloir means a 2nd-3rd degree climb, though you shall often find it covered by snow.
Total climb: 1160 meters from the car park to the summit
No special needs for summer season, though walking poles might be handy for the final climb from Brecha de Aísa to the summit. Winter season shall require full winter equipment, including warm clothing, crampons, ice axe and so on.