From Girona · 41.98° N · 2.82° E
Three getaways with a night away and four day trips from Girona for 11 September, the Diada: the Penedès, Empordà and Priorat harvest, the medieval Empordà as calm returns, Besalú and Castellfollit, and Montserrat on horseback before autumn.
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The Diada falls in the middle of the Penedès harvest, when the cellars work day and night with the grapes coming in. The hotel serves its gastronomic menu on the eve of the holiday: book the table for 10 September along with the room.

In September the stone villages of the Baix Empordà empty of summer people and the sea is still warm. From September to February the balloon goes up only at weekends: if the 11th falls midweek, it flies on Saturday.

In September the Empordà vineyards are in harvest, and the Perelada winery shows the grapes coming in. The Dalí Theatre-Museum moves off summer hours: buy a timed ticket and start there first thing.

In September the Priorat garnacha is harvested and the kayak on the reservoir opens on autumn weekends. The 4x4 route among vineyards goes out with a single vehicle: book it before the room.

After the Besalú Medieval festival, at the end of August, the village returns to calm and in September it is strolled without the heat. The fortified bridge and the Jewish quarter are seen on foot, and Castellfollit is fifteen minutes away.

On harvest Sundays the Penedès wineries with tables fill, and a holiday in September is like a Sunday. Book the visit and lunch with days to spare, and go by train: that way nobody drives after the tasting.

September opens the good season for horse riding at the foot of Montserrat, without August's heat. The Escolania sings again after its summer holidays; the rack railway from Monistrol goes up in a quarter of an hour.
Questions
Yes, 11 September is a holiday across Catalonia.
Yes: in September the Empordà, Penedès and Priorat wineries are in full harvest. Book the timed visit.
Geocaliahttps://www.geocalia.com/en/spain/catalonia/girona/getaways/diada-long-weekend