A ringfort, or rath, was typically a circular earthwork enclosing a farmstead, constructed during the early medieval period and used by farmers and their households for centuries. What makes the one at Crohane quietly odd is not what it has but what has happened to it: a large open-cast quarry, roughly 30 metres by 15 metres and two metres deep, has been scooped out of the north-eastern interior, leaving a monument that has been both exploited and obscured. Thorn bushes and scrub now cover much of what the quarry did not claim, making any close inspection of the interior effectively impossible.

The earthwork itself is a platform type, meaning it was deliberately raised above the surrounding ground rather than simply enclosed by a bank. That elevation was practical; the valley was originally wet and marshy, and raising the living platform above the waterlogged ground would have been essential. The structure survives as a circular raised area approximately 26 metres across, defined by a scarp between 0.8 and 1.4 metres high and an outer fosse, the ditch that ran around its base. A later field boundary bank cuts across the monument on its northern side, and two further field boundaries intersect it at the east and west, all of them visible on the Ordnance Survey six-inch map of 1903. The quarrying that damaged the north-east quadrant of the interior most likely dates from the nineteenth century, the same period that produced the sharp-profiled boundary bank. The land to the north and south was drained and reseeded in grassland roughly fifteen years before the monument was recorded, though the ground immediately to the west remains wet and undrained, giving some sense of the boggy conditions the original builders were working around.