This finger of rock juts northward from steep cliffs into Cooncrome Harbour on the Iveragh Peninsula in County Kerry, and for its first fourteen metres from the landward side it measures just four and a half metres across. It is the kind of place where the sea does much of the defending work, and whoever built here clearly understood that.

The fort's engineering is methodical and, in places, quietly impressive. A promontory fort is a type of prehistoric or early medieval enclosure that uses a coastal headland as its main defensive boundary, cutting off the landward approach with earthworks rather than encircling the entire site. Here, two banks and their accompanying fosses, ditches cut into the rock, run across the promontory at the point where it widens slightly, and the deeper of the two is rock-cut to a depth of 2.3 metres with a flat-bottomed base under a metre and a half wide. Between these barriers, a causeway just one metre wide and seventeen metres long provided the only way in. At its inner end, two upright portal-like slabs set just over a metre apart marked what appears to have been a formal entrance, and a large prostrate slab lying directly to the north may once have served as its lintel. When the antiquarian Chatterton visited in 1839, he noted that upright stones still lined the full length of the causeway; by the time T. J. Westropp recorded the site in 1912, coursed masonry piers flanked the inner portal, though none of that facing survives today. Inside, the ground slopes down sharply to the northwest, and a natural ridge of outcrop about 1.2 metres high runs along the eastern edge of the interior, adding one more layer of protection that the builders appear to have incorporated deliberately into the design.