Annaghkeen Castle is a late 13th century hall-house and is thought to be Ireland's oldest example of a castle built entirely from undressed stone. It was built along with the nearby Cargin Castle by the Norman DeBurgo family to defend the Manor of Headford from incursions across Lough Corrib by the rival O'Flaherty clan.
The DeBurgos ('Burkes') became more completely Hibernicised than any other Norman family in Ireland. They proclaimed themselves chiefs in the old Irish fashion and adopted Brehon Law, the indigenous system of law dating from Celtic times. Their long running feud with the O'Flaherty clan stems from the DeBurgos arrival in Galway when they disposed the O'Flahertys of their lands and then tried to lease them back to them. When no rent was paid one of the DeBurgo clan was sent to the O'Flaherty stronghold at Aughanure Castle in Oughterard to collect payment.
When he arrived at the castle the O'Flahertys were feasting on a banquet and he was invited to join them. The DeBurgo man enjoyed the hospitality and during the feasting he mentioned the rent at which point an O'Flaherty pressed down on a concealed flagstone which hurled DeBurgo into the river. Living up to their name as the 'Ferocious O'Flaherties', they then cut off his head and sent it back to the remaining DeBurgos, describing it as "O'Flaherty's rent".
The ruins of an early 19th century three bay, three storey gable ended manor house with half hexagon central bay stands in an open field between Annaghkeen Castle and shores of Lough Corrib.