This type of monument, known as a promontory fort or cliff castle, required comparatively little construction effort precisely because the landscape did most of the work. The occupants, cut off on three sides by sheer drops and Atlantic water, needed only to defend the landward approach.

Dunlough itself sits in one of the more remote corners of Cork, a place where the peninsula narrows dramatically before meeting the sea near Three Castle Head. That nearby site, with its unusual cluster of medieval tower houses beside a lake perched above the ocean, has drawn most of the attention in this area, but the promontory fort represents an altogether older layer of human settlement. Coastal promontory forts in Ireland are generally associated with the Iron Age, roughly the last few centuries before the Common Era, though some were reused or adapted in later periods. Their builders chose headlands for the same reasons that would appeal to any defender: visibility, isolation, and the sheer difficulty an attacker would face approaching from the sea.