From Tarragona · 41.12° N · 1.24° E
Three getaways with a night away and four day trips from Tarragona for 11 September, the Diada: the end of summer in the high mountains, from the Tristaina lakes to Añisclo and Núria, the Penedès harvest, Siurana kayaking, the Coll de la Creueta and Montserrat on horseback.
Map

September is the last month of the Tristaina lakes free of snow, and the 11th is not a holiday in Andorra, so Ordino is quiet. Bring your ID card, start the lake circuit early and leave Caldea for the afternoon.

In September Añisclo returns to its good season, with fewer cars than in August, and the 11th is a working day in Aragon. It is three hours from Tarragona: two nights, and Sunday's canyon, booked before leaving.

In September Núria has meadows still green and the Rack Railway still on summer hours. The Diada is celebrated in the Ripollès with sardanas in the morning; buy the train online, as the holiday fills.

The Diada falls in the middle of the Penedès harvest, and on harvest holidays the wineries with tables fill. Book the visit and lunch with days to spare; from Tarragona you get there by train with a change at Sant Vicenç.

In September the kayak on the Siurana reservoir is still open and the Trona begins to be done without August's sun, best first thing. Book lunch inside the village, which is closed Tuesday and Wednesday.

September is one of the best months for the Coll de la Creueta, at 1,921 metres, without August's traffic or spring's gravel. Fill the tank in Berga and come down before the afternoon storms.

September opens the good season for the horse ride at the foot of Montserrat, without summer's heat. In the afternoon, at the sanctuary, the Escolania is back from its summer holidays.
Questions
No: only in Catalonia. That is why the Andorran lakes and Añisclo are quieter that day.
Usually, with cold mornings and the odd afternoon storm. It is the last month with the lakes free of snow.
Geocaliahttps://www.geocalia.com/en/spain/catalonia/tarragona/getaways/diada-long-weekend