Kildavnet Castle is a 15th-century Irish rectangular tower house strategically guarding the waters of Achill Sound, which links Blacksod Bay and Clew Bay. It is best known as one of the strongholds of Granuaille (Grace O’Malley), who controlled much of County Mayo. 

She became chieftain of the O'Malley clan on the death of her husband and soon gained a reputation for successful business and piratical activities, such as raiding other clans territories and collecting taxes from passing ships.