Derrinlaur Caslte, Derrinlaur Lower, Co. Waterford

The castle's recorded history stretches back to 1520, when the powerful Butler and Power families were locked in a dispute over its ownership, though the fortress itself may well be older. The castle's strategic position made it a prize worth fighting for during the tumultuous 16th century. In 1574, John Fitzgerald, Earl of Desmond, seized the stronghold during his rebellion against English rule, only to lose it the following year when Viceroy Sir William Fitzwilliam recaptured it and massacred the rebel garrison within its walls.

By 1640, the once-formidable fortress had fallen into disrepair, described in contemporary records as merely "the stump of a castle" belonging to Thomas Butler, Lord Cahir. Despite its ruined state, the castle was still considered significant enough to be carefully documented in the Down Survey maps of the 1650s, which recorded land ownership across Ireland following the Cromwellian conquest.

What remains today is an impressive circular tower, roughly 11 metres in diameter and originally standing about 15 metres tall, complete with defensive base-batter, buttresses, and machicolations from which defenders could rain down projectiles on attackers below. The tower's interior chambers are all circular, a design feature that maximised structural strength. At some point, a rectangular structure with circular corner towers was added to the west and south sides of the main tower, though only the southeast corner tower survives; a modest 7.4-metre diameter structure standing about 4 metres high. Recent archaeological testing of the surrounding area in 2007 found no additional artefacts, suggesting the castle complex was relatively self-contained within its defensive walls.