Built in 1210 for King John of England, this mighty stone fortress sits on the edge of the Shannon, atop the ruins of an earlier fort built in 1129 as the seat of the chiefs of Connaught. Besieged for almost 6 months in 1641, the castle was attacked again in 1690 and finally fell in 1691 after an intense bombardment by forces sent by William of Orange. The fall of Athlone was a key event in the war that would cement the Protestant establishment in Ireland and ensure British rule, all the way up to the War of Independence in the 1920s. (The Dutch military commander who took the town, Godard van Glinkel, was rewarded for his efforts with the earldom of Athlone.) Three centuries later, in 2012, the castle underwent a multimillion-euro renovation; it now houses eight separate galleries on the history of Athlone, particularly the 1690-91 siege, using plenty of high-tech wizardry. The castle’s original medieval walls have been preserved, as have two large cannons dating from the reign of George II and a pair of 25cm (10-inch) mortars cast in 1856.