The impressive ruins on the remote Rinnduin Peninsula at Lough Ree have quite a romantic appeal, though they are very overgrown and frustrating to study. The first castle and town was founded here by Geoffrey de Marisco in 1227 as a base during his campaign west of the Shannon. Once the Normans secured a greater foothold in Connaught, Rinnduin assumed an increasingly important position in government military strategy. By the 1270s it was providing a vital link between the royal forts of Roscommon and Athlone, as well as guarding the ships along the Shannon and helping to keep the O'Connor kings of Connaught in check.The castle is protected by a wide moat, once filled with water, running across the peninsula. This was probably dug in 1227, but the ward wall behind, which has small square loopholes, may not have been completed until 1260. The ward was entered through a rounded-headed archway of cut limestone with slots for a portcullis, outside of which are masonry piers for a bridge that was repaired in 1278. A town developed under the protection of the castle, defended on the landward side by a substantial towered wall. Only the ruins of the parish church remain, to the east. The town was sacked by the O'Connors in 1236 and 1270. After its final plunder in 1315 it appears not to have recovered.
17.5 km (11 miles) N of Athlone and 4 km (2.5 miles) E of Lecarrow. Access through fields for half a mile to end of peninsula. NGR: N 008539.