Congratulations to Jamey who guessed drying shed!
These “unofficial symbols” of the Galicia region of Spain are known as horreos. We were told they were used to dry corn and sure enough, when we peeked inside we saw corn.
Traditionally, farmers stored and dried grain within the horreos. Sadly, they no longer offer practical storage for modern day farmers, but horreos remain popular with landowners who feel they are a valuable historical feature.