PORTUMNA CASTLE Portumna Castle and Demesne occupy a magnificent location on the shores of Lough Derg on the River Shannon. Although gutted by fire in 1826, the Castle is still an imposing example of Irish architecture of the early 17th Century. Built before 1618 by Richard de Burgo, 4th Earl of Clanricarde, the castle became the main seat of the de Burgo family for over 200 years.