The gap is the most animated feature of Cashlaunagur Fort, a rath sitting at the north-western end of a low natural scarp in the townland of Carrowreagh. A rath, for those unfamiliar with the term, is a roughly circular enclosure defined by an earthen bank and ditch, built during the early medieval period in Ireland and typically associated with a farmstead or small settlement. This one commands views in every direction, a placement that was almost certainly deliberate.

The structure appears on Ordnance Survey six-inch maps from both 1838 and 1929 under the name Cashlaunagur Fort, suggesting the site was already well established in local consciousness by the time those surveys were made. The raised circular area measures roughly 21.5 metres east to west and 23.6 metres north to south, enclosed by a bank of earth and stone approximately 3.5 metres wide. The bank's internal face is relatively low, rising only between 0.3 and 0.5 metres on the inside, while the external face reaches 0.9 metres at the south-east and a more emphatic 1.5 metres at the north-west, where the natural fall of the ground adds to its height and steepness. Stones break through the turf along the bank's top and sides. The interior is level and gives nothing away, offering no visible features to suggest what once stood within. Attached to the north-east of the rath bank is the faint outline of a roughly square area defined by the remnants of a field bank; this appears to be a comparatively recent addition, a small plot that someone later pressed into use alongside the older monument.