This rectangular tower, measuring 10 metres east to west and 6.6 metres north to south, survives only to its first storey today, with most of its eastern wall having succumbed to time. The castle once belonged to the Condons, a Norman family who established themselves in this part of Cork during the medieval period.

The tower’s ground floor reveals fascinating architectural details despite its ruined state. The original entrance was positioned near the northern end of the east wall, though only the door rebate remains visible along the eastern end of the north wall. Inside, the main chamber spans approximately 5.45 metres by 2.85 metres and was once covered by a barrel vault running east to west; only the vault’s springings survive today. Natural light entered through central windows in both the south and west walls, each featuring wide, square embrasures topped with segmental vaults, though the actual window openings have long since vanished. The southern embrasure has been enlarged into a doorway at some point in the castle’s history.

Small details hint at the domestic arrangements within this defensive structure. The remnants of a garderobe chute can be spotted at the eastern end of the north wall, providing evidence of medieval sanitation. The castle has suffered from stone robbing over the centuries, with quoin stones particularly targeted at the northwest and southwest corners, leaving the structure more vulnerable to decay. Standing roughly 100 metres above the river below, Ballynahow Castle would have commanded impressive views of the surrounding countryside, serving both as a residence and a strategic stronghold for its Condon lords.