The earthwork, roughly 55 metres in diameter, is defined by a rise of only 0.35 metres along its southern and eastern arc, less a wall than a whisper in the ground. A ringfort, or rath, was typically a circular enclosure bounded by an earthen bank and ditch, used as a farmstead or defended homestead during the early medieval period, from roughly the fifth to the twelfth centuries. This one has been further diminished by infrastructure: the Cobh reservoir cuts directly into its south-eastern quadrant, erasing part of what was already a subtle outline.

The site was recorded as early as 1904, when Healy placed it on top of Carrignafoy hill, one field west of what was then described as the reservoir of the Queenstown water supply, Cobh having been known as Queenstown under British administration until 1922. That the fort was detectable at all in the twentieth century owed something to aerial photography, through which Dr D.D.C. Pochin Mould identified it as a shadow site, a category of archaeological survival visible only from the air, when low sunlight or differential crop and soil growth betrays the ghost of a vanished or heavily degraded structure beneath the surface. The combination of a near-invisible earthwork and a reservoir eating into the perimeter makes this one of the more quietly compromised prehistoric survivals in east Cork.