The Pilar Festival is held every year around the second week of October in Zaragoza .
The festival features a huge flower offering on October 12 th in which thousands of flowers are piled into a gigantic pyramid in the center square next to a huge basilica.
It's a great photo op.
; here's a (not so good) picture I took of the flower pyramid from last year's festival: The festival is also accompanied by a number of cultural performances, parades, concerts, bull fights, &c. Edit :
In terms of weather, it depends what you're looking for.
I've been all around Spain in different seasons, but when I was there last fall we primarily toured in the North
(Madrid → Zaragoza → Atxondo → San Sebastian/Bilbao → Elciego/Rioja → Segovia → Madrid).
About 10% of the days there was rain, and it would sometimes drop down to the mid-teens (Celsius) at night, but it was generally quite pleasant weather.
I wore a light jacket most of the time.
The South would have been noticeably warmer.
travel.stackexchange.com/users/130/ESultanik
You are looking to walk the Camino de Santiago .
It joins hiking, nature, historic architecture, photo opportunities and is very cheap (eat about 6-8 € per meal and sleep 4-8 €).
Additionally, you'll know the real Spain, meet interesting people (mainly Spanish, but you can find people from around the world and you will complete one of the mythical mid age routes.
Depending on the time you have you can start from one city or other.
For instance if you have 2-3 weeks you can start walking from Leon.
Fall is a great moment to go.
Spring is better, but winter and summer are worst because the extreme temperatures.
travel.stackexchange.com/users/1425/Ivan
One thought if you can do end of August - La Tomatina in Bunol near Valencia is quite the fantastic photo opportunity, as is the wine and water festival in La Requena nearby the night before ;)
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Spain has a wealth of hiking areas, Asturias, Cantabria, Galicia and the Basque Country offer amazing landscapes.
Some people call them the Switzerland by the Sea.
Sites worth visiting for hinking, landscaping and taking photographs:-
Cordillera
Cantábrica1.
Lagos de Covadonga (Asturias) Senda del Oso (Asturias) where you will be able to see bears while hiking or biking.
I recommend you to stop in the coastal cities/villages of Gijon, Cudillero and Llanes (really good cuisine plus beautiful sites).
GaliciaI really recommend to visit Islas Cies, this is a set of islands really well preserved where you can enjoy a wonderful landscape and routes for hiking and a cold but a refreshing bath in its clear blue waters.
The Pyrenees and the Ebro region are Spain’s most popular and accessible hiking regions, assisted by the abundance of winter sports resorts and ski-lifts that whisk you to the mountain tops.
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Cabo de Gata in Almeria is a good place to get in touch with nature.
You have a lot of natural sights, you can do scuba diving, hiking and so on.
Besides the weather in September and October usually is quite good.
http://g.co/maps/buvn6 http://www.parquenatural.com/galeria
travel.stackexchange.com/users/1779/Sergio
The Pyrenees mountains are a great choice for hiking and nature sightseeing.
In particular, the catalan side north of Barcelona, where the mountain meets the sea is worth a trip and thousands of photos.
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I'm thinking about visiting Spain sometime in September or October.  I'm interested in hiking, nature and historic architecture and am constantly looking for great photo opportunities.  Which parts of the country would be most suitable for me in terms of weather and sights?
Good locations in Spain for hiking, nature, architecture, and photo opportunities?
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<planning><sightseeing><nature-and-wildlife><spain><hiking>
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You could walk the Camino de Santiago, get in touch with nature in the Cabo de Gata in Almeria or go hiking and nature sightseeing in the Pyrenees mountains. Asturias, Cantabria, Galicia and the Basque Country offer amazing landscapes for hikers, while the coastal cities/villages of Gijon, Cudillero and Llanes have really good cuisine plus beautiful sites . La Tomatina in Bunol near Valencia is quite the fantastic photo opportunity at the end of August, as is the wine and water festival in La Requena nearby the night before. Places like The Camin de Santiago, Cabo de Gata and The Pyrenees mountain are great choices to get in touch with nature.
Places like The Camin de Santiago, Cabo de Gata and The Pyrenees mountain are great choices to get in touch with nature. Whilst, La Tomatina in Bunol near Valencia  Asturias, Cantabria, Galicia and the Basque Country, coastal cities/villages of Gijon, Cudillero and Llanes all offer amazing landscapes that are great photo opportunities.  La Tomatina in Bunol near Valencia  Asturias, Cantabria, Galicia and the Basque Country, coastal cities/villages of Gijon, Cudillero and Llanes all offer amazing landscapes that are great photo opportunities. 