The five-storey limestone structure rises from a modest base, its walls built from roughly coursed rubble with a distinctive batter at ground level. Built by the Shortall family who had been associated with Clara Upper since the 13th century, dendrochronological dating of the oak beams has revealed precise construction dates, with timbers felled in spring 1523 and work continuing through the 1540s. The castle remained in Shortall hands until around 1642, after which it passed through various owners including the Cromwellian grantee Henry Johnson and the Byrne family, who occupied it until the early 19th century.

The tower house measures approximately 10 metres by 8.2 metres and features the classic defensive elements expected of such structures. Entry is through a pointed doorway on the north side, originally protected by a murder hole above and a machicolation at parapet level. Inside, a spiral staircase in the northeast corner connects all five floors, each serving different purposes; from the ground floor guard room to the upper chambers with their timber floors supported by wall corbels. The second floor contains particularly fine architectural details, including a hooded fireplace with a flat arch supported by slender tapering corbels, whilst hidden within the third floor lies a secret mural chamber, or oubliette, concealed behind a false garderobe with only a small square opening for light and air.

What makes Clara Castle particularly fascinating is evidence of late 16th or early 17th-century modifications, especially visible at the fourth floor where the original spiral stair was removed and replaced with a new access arrangement. The castle underwent thorough repairs in 1929 under the supervision of architect Harold Leask after being vested in the Commissioners of Public Works. Today, visitors can still see the stepped crenellations of the well-preserved parapet and the small forecourt or bawn that once protected the entrance. The surrounding landscape offers restricted views to the east and north due to Grange Hill and Oliver’s Hill, though Freestone Hill remains visible to the southeast, with a stream running roughly north to south about 100 metres to the east of the castle.