While Oughterard was home to an important Anglo-Norman manor and borough, no early documentation mentions a castle here until 1636, when records note that one John Alen died holding a castle and ten messuages at this location. The structure itself, however, tells a more complex story through its weathered limestone walls.

The tower measures approximately 7.2 metres in length and 5.5 metres in width, built from roughly coursed rubble limestone masonry with three distinctively rounded corners at the north, east and south. Its most intriguing architectural feature is the projection at the western corner, where the southwest wall extends 2.5 metres beyond the main building; likely the remnants of what once enclosed an external stairway. The ground floor, covered by a barrel vault, is accessed through a partially robbed doorway with a segmental arch on the northeast wall. Light filters in through irregular double-splayed loops in the northeast and southwest walls, with an additional narrow loop at the western corner. Above the vault, two more floor levels survive, though curiously there’s no obvious internal access to these upper floors, suggesting the external stairs at the western angle provided the only means of reaching them.

The castle’s defensive elements include a shallow machicolation supported by three corbels on the northeast wall at second floor level, while its domestic arrangements featured a fireplace in the northeast wall and corbels indicating where a loft once sat beneath the vault. In later years, the third floor underwent an unusual transformation when it was partially converted into a dovecote. Today, visitors can still spot the narrow string course with drain holes at wall walk level and the remnants of low parapets that once crowned this enigmatic tower, which stands as a testament to the layered history of medieval Kildare.