The feature is called Poulaninneen, from the Irish Poll na nIníonach, meaning the hole of the daughters. A note recorded in the Ordnance Survey Name Books of 1841 describes it as a deep cavity through which the sea passes by a subterranean channel, and records the local tradition that the owner of Pookeenee Castle, fearful that his nine daughters' chastity would be violated, cast them into it to their deaths.

The site itself is a promontory fort, a form of coastal enclosure in which a headland is defended on its landward side by one or more banks and ditches, with the sea acting as a natural barrier on the remaining sides. Here, the earthen bank and fosse, the ditch dug to reinforce it, run for approximately 70 metres in a line slightly convex toward the land, cutting off a promontory that measures around 140 metres north to south and 92 metres east to west. At some later point, Pookeenee Castle was built within the line of these older defences, making the fort's bank do double duty as a boundary for the medieval structure that followed. A fieldbank running in a north-west to south-east direction also cuts through the site, adding another layer to the accumulated occupation of the ground. The blow-hole itself sits in the south-western sector of the promontory, where the sea's passage beneath the rock occasionally forces air or water upward through the opening, the kind of geological feature that tends to attract local legend and, in this case, preserved a story of unusual darkness well into the nineteenth century.