The site features a distinctive motte and bailey castle, with its flat-topped earthen mound rising 2.5 metres above a D-shaped bailey that stretches approximately 100 metres across. The motte itself, measuring about 11 metres across its top, would have once supported a wooden tower or fortification, whilst the surrounding bailey provided space for buildings and activities within the protective enclosure. Today, these grass-covered remains sit on a gentle rise overlooking a small stream, with the site of the old parish church about 500 metres to the west.

The Parys family held these lands from at least the fourteenth century, with Edward Perers recorded as possessing two carucates here in 1385. Their tenure wasn’t without drama; Christopher Parys joined the rebellion of Silken Thomas in 1534, and whilst the family initially recovered from any forfeiture, George Parys’s later conspiracies with O’Connor of Offaly around 1550 proved their undoing. The Crown confiscated Agher and granted it to George Gernon of Louth, who cleverly managed to retain it despite Parys’s reconciliation with the authorities by 1552. The Gernons developed the property significantly, and by 1621 Anthony Gernon held a castle, multiple buildings, and 440 acres here. The Civil Survey of 1656-8 recorded George Gernon’s holdings as including not just the castle but also a church, pigeon house, and various cabins across 425 acres.

After the Cromwellian period, the estate eventually passed to Benjamin Pratt from Leicestershire before transferring through marriage to the Winter family in the mid-eighteenth century. The Winters, who became the parish’s principal family well into the nineteenth century, likely built Agherpalis House (now demolished) and created landscaped gardens that drew considerable attention in their day. These gardens stretched mainly west of the house, though the medieval earthworks to the southeast and southwest were probably incorporated into the designed landscape. Archaeological evidence suggests a deserted medieval settlement immediately northwest of the outer bailey, with remnants of an old field system extending southwest, painting a picture of a once-thriving medieval community centred around this imposing fortification.