Ballyhack Castle commands an imperious position on a steep-sided valley overlooking Waterford Estuary. It is thought that the Knights Hospitallers of St John, one of the two mighty military orders founded at the time of the Crusades, built this sturdy tower house around 1450.

The tower is five stories tall and the walls survive complete to the wall walk. Built into the north-east wall of the second floor is a small chapel complete with a piscina, aumbry and altar. The entrance to the castle is protected externally by a machicolation and internally by a murder hole - that is, an opening through which defenders could throw rocks or pour boiling water, hot sand or boiling oil, on anyone foolish enough to attack.