I'm not sure if this should be classed as a building. But rather than start a 'folly, or bizarre seemingly useless construction' list, I thought I'd lump it in with the buildings.
I've seen this square shape in the hills many times while driving southwards from town, but never actually got close to it. On a dog walk yesterday, I discovered after a wrong turning that I was approaching afore-mentioned square object.
It sits on the crest of a hill, guarded by two giant rabbit ears of cypress, facing the distant snow-covered Pyrenees. Built of various types of stone and Toulousian brick, it is topped by nothing: no statue of Christ, no bronze sculpture of famous local wine maker. It has no door, no interior, and no plaque stating why it is there.
I might go back each week and place a different item on top, a sort of changing installation, but as no one apart from me and a few disinterested sheep will notice, perhaps not.