Kilcashel Stone Fort
Ireland
Kilcashel Stone Fort is a double court cairn and National Monument located in County Mayo, Ireland, 800m (½ mile) southeast of Kilmovee. The last surviving member of three stone forts in the area, it's estimated to have been constructed between 2,500 and 500BC.
Monument data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).