Hay Barn in Farmstead World — building in the game, and what it is on a real farm.
A hay barn keeps bales under cover, because hay that gets wet heats up, moulds, and can even catch fire in the stack.
The building is left open at the sides or the ridge so air moves through the bales and finishes drying them.
Farm facts about hay barn
In the United Kingdom, a 'Dutch barn' is an open-sided shelter for hay stacks; the version with a movable roof is called a 'hay barrack' in the US. (en.wikipedia.org)
Hay stored with more than about 25% moisture can catch fire all by itself: bacteria and mold ferment the damp hay, trapped heat builds up, and the stack can ignite within weeks. (en.wikipedia.org)