Built sometime between the late 15th and early 16th centuries, this circular fortress was likely constructed by the Butler family to control this strategic river crossing. While some historians once believed an earlier 12th to 14th century castle occupied this exact spot, archaeological excavations in 2003 and 2004 revealed the walls of a substantial 13th or 14th century building about 100 metres to the east, just south of the bridge, which was probably the original castle mentioned in historical records.

The tower house saw dramatic action during the 1641 Rising, when more than 120 men, women and children endured an eleven week siege within its walls. By 1640, according to the Civil Survey, the castle and bridge belonged to James, Earl of Ormond, who held the lands of ‘Goulden’. When Ordnance Survey officials visited in 1840, they found the structure still intact; a round tower roughly sixteen feet across inside with walls nearly six feet thick, rising about fifty feet high with three floors, the uppermost supported by a stone arch.

Today, only the eastern half of the tower survives, though it still offers fascinating glimpses of its defensive architecture. The remaining structure preserves the ground to first floor spiral staircase, along with portions of the second and third floors. The ground floor appears to have been vaulted, whilst two cut limestone gun ports face east and southeast, with one positioned to guard the stairwell. Two arrow loops point east and northeast, and a single light window with an elegant ogee arch graces the third floor level. A string course marks where the parapet once began, complete with drainage holes above to channel rainwater away from the defenders below.