2Dún Aonghasa – Ireland (circa 1100 BC)

Perched on the edge of a dramatic sea cliff on Ireland’s Aran Islands, Dún Aonghasa is a prehistoric fort that predates most traditional “castles” by centuries.

Though not a castle in the medieval sense, its stone walls and defensive layout served the same protective purpose for the island’s ancient Celtic inhabitants. With views stretching across the Atlantic, it’s one of Ireland’s most mystical historical sites.

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