The four-storey castle, measuring approximately 11.8m by 8.6m and rising to 18.3m in height, features distinctive architectural elements including four gables, lofty chimneys, and circular bartizans on the northeast and southwest corners. Built during the final phase of the tower house tradition in Limerick, likely during the reign of Elizabeth I or James I, the structure exemplifies the defensive architecture of its era with its battlements, spiral staircase in the southeast corner, and strategically placed two-light windows adorned with hoodmoulds.

The castle’s history is deeply intertwined with the powerful Butler and O’Brien families who controlled this strategic location near the Tipperary border. The 1654-7 Civil Survey records that James Butler and his widow Mary owned what was then described as ‘a Mill and a broken Castle’ in the townland of Pollardstown, as the area was known. The site’s importance stretches back even further; in 1282, the lands of Welese were granted by the citizens of Limerick to J. fitzThomas, and by 1572, Tirrelagh mac Brien held a castle at Knockowlow, the earlier name for Oola Hills. Local folklore adds a colourful dimension to the castle’s construction, with stories passed down through generations claiming the mortar was mixed with bullock’s blood and milk curds, supposedly accounting for the structure’s remarkable durability.

The castle doesn’t stand alone in its historical significance; the surrounding landscape tells a broader story of medieval settlement. Extensive earthworks to the north and west suggest a deserted settlement once thrived here, whilst Oola Church and its graveyard lie just over a kilometre to the west. The tower’s robust construction has allowed it to survive in reasonable condition, with its upper levels still displaying fireplaces in the east and west walls, though the original entrance has long been blocked. Today, this atmospheric ruin serves as a tangible link to centuries of Irish history, from medieval land grants through Elizabethan conflicts to its eventual abandonment, all whilst maintaining its commanding presence over the Limerick countryside.