Looks like a prison to me. Isolated location, multiple walls/fences, guard towers at the corners. If it were military you'd see much more activity. Also, notice the parking lot? Notice all parking is outside the fence? Military bases have parking/motor pools inside the fence line. Also, there is no obvious HQ building with the associated flag poles and VIP driveway leading to the front door.
Got it. This is the "Centro Penitenciario La Moraleja", on highway P-120 outside Duenas.
Here's a http://www.mir.es/instpeni/sggestion/sgg_casleon.htm>more info link. Scroll down to Centro Penitenciario La Moraleja, there's a picture there, taken from the east courtyard (with the diamond in the center) from the north side of the yard looking east towards the guard tower. Beyond the gate you can see the northernmost building of the center section.
I can confirm that this is La Moraleja Prison in Duenas, Palenia.
I was an inmate there for 2 years. In Spain there ar no penal informs, and we had sports centres, gems, swimming pools and 7 am. Till 8 pm out of our cells.
Prisons 
My guess is a prison.
Googling only got me this:
http://www.lasalle.es/valladolid/martires/prision.htm
Vallodolid is a town near the buildings. The site shows a prison with inmates playing soccer. Probably just coincidence!
Here's a http://www.mir.es/instpeni/sggestion/sgg_casleon.htm>more info link. Scroll down to Centro Penitenciario La Moraleja, there's a picture there, taken from the east courtyard (with the diamond in the center) from the north side of the yard looking east towards the guard tower. Beyond the gate you can see the northernmost building of the center section.
Thanks to http://www.mapquest.com/maps/map.adp?ovi=1&mqmap.x=404&mqmap.y=215&mapdata=WG87d0DdSaqV%252bsE6WXdITGGz5%252b8ISTf%252bMUvg6zG3W8Hhwvgis6SQGQgWjGpLga2RRXDaY2RdXV7C8stZ0K2ZQQnsnubRnwW%252bcGfoJ7SaTgYRhKo3apgCNkt4liDSo7CJqY%252buMfcDwQzY%252biPh36NcisAh0qbLfMQVMaMIaJZOzoaYhHra4LGtfMiZ8dw0Fuc9o50DGn6yfjNcp7Ie8ErKCxbD0hzPsypXUvi85P1jjO2f2B3flYnP08WEViTdUSk1zKXVfR6m00dd5hGurzYsIWJnSsZ3K%252f%252bOUZpz4vs6KDOExTW3NbbvfqaxtPSeFcOYO0l%252fQpyos3dEQ%252fG5fNuu7mrDLs7iVoGU7wDT4bKshDl%252bRvEt6%252bGXkguV%252bpodPZB2kX4EAB%252bMoEi3voteyPkK8Do5UNWTplWSRGdH78QH6%252bspNnUBm4OY3Vae6gHcR3q4H%252b%252fPznyE0KqX0Vq1J3h0%252bXOz7FtZdYQettRAtbbPzwjrNJmrm6BO0w%253d%253d>Mapquest and http://www.google.com/search?hl=en&lr=lang_en&q=duenas+p-120&btnG=Search>Google
I was an inmate there for 2 years. In Spain there ar no penal informs, and we had sports centres, gems, swimming pools and 7 am. Till 8 pm out of our cells.