Built in 1227 by Turlough O’Conor and Geoffry de Marisco, the castle likely replaced an earlier earthwork fortification, which would explain its unusual triangular shape. The structure saw considerable action during its early years, suffering attacks in 1270 and 1272 that left it severely damaged, though repairs were swiftly carried out between 1273 and 1278. A new hall was added at the turn of the 14th century, but by 1342 the castle had fallen into Irish hands and gradually slipped into obscurity, remaining largely forgotten until George Goodman acquired it in 1578 and attempted some restoration work.

The castle’s design reveals clever medieval engineering adapted to its triangular site. The keep, of which only the northwest section survives, originally featured two barrel-vaulted chambers on the ground floor, with a mural staircase providing access to the upper levels. The triangular ward measures approximately 64 metres from northeast to southwest and 34 metres from northwest to southeast, enclosed by curtain walls that still stand almost complete on the southern side. Rather than building expensive corner towers, the medieval builders opted for an ingenious solution; they installed two rows of putlog holes to support wooden hourds, projecting timber defences that could protect the walls just as effectively. The 16th-century repairs added multiple gun loops throughout the structure, adapting the castle for the age of gunpowder warfare.

Today, this registered monument tells a complex story of Norman ambition, Irish resistance, and centuries of conflict and adaptation. The attached hall, possibly the ‘new hall’ mentioned in records from 1299 to 1302, features a fireplace, multiple embrasures, and intriguingly, evidence of what archaeologists believe was a timber garderobe tower projecting from the northwest wall. A defensive fosse, originally crossed by drawbridge, surrounded the castle, whilst remnants of an outer barbican can still be traced in the grass-covered cairns near the entrance. Despite its current overgrown and unsafe condition, Rindown Castle remains an important piece of Ireland’s medieval heritage, offering insights into the military architecture and turbulent politics of 13th and 14th century Connacht.