We went to Northern Spain in late September and early October, 2016. It was sort of a spur of the moment trip due to the unexpected cancellation of other planned trips. In additional to visiting Barcelona, we were hoping to do some hut-to-hut hikes in the Pyrenees. Unfortunately, most of the huts in the Pyrenees are closed at the end of September. So we settled on going to the Refugio Goriz in the Ordesa National Park, which is one of the few huts that are open all year round. In theory, we could also hike from Goriz to Gavarnie (France); the hut in Gavarnie is open on weekends. But quickly we figured out the logistics for such a hike is too daunting, such as timing for the weekend and how to get back from France to Spain - the public transportation in these areas is not well-developed (unlike Switzerland). So we settled on going to Goriz and do day hikes from there.
We flew to Barcelona and spent a couple of days there. Then we rented a car to drive to the eastern entry of the
Ordesa National Park in Aragon
from which we hiked to Refugio Goriz. After spending two nights in the hut, we hiked back and drove to the Valle de Pineta on the western edge of the Ordesa Park. We stayed in Parador de Bielsa and did a long loop trail there. From there, we drove to the Serra del Montsec region and did some birding. After that, we drove back to Barcelona, dropped the car off at the airport and spend the rest of our trip in Barcelona.