What makes it quietly odd is that the ground does not level out as you pass through; it rises noticeably from the outer archway toward the interior, so that anyone entering the enclosure is walking uphill through the gate itself, with the paved causeway still partly intact beneath their feet. That original paving has survived, which is itself unusual. The building measures roughly 4.9 metres by 5 metres internally, with round granite arches to the north and south, and the arches reach 3 metres from the ground to the soffit, giving the passage a proportional solidity that reads as deliberate rather than merely functional.

The structure was formerly two-storied, which placed it in the tradition of monastic gatehouses that combined controlled access at ground level with a room or watch-space above. The upper floor no longer survives, but its existence is indicated by corbels, small projecting stones built into the interior walls to support the timber or stone of the floor above. The walls also feature antae, the projecting pilaster-like extensions of the side walls beyond the end walls, a feature more commonly associated with early Irish churches than with gates, and one that gives the building a slightly ecclesiastical character appropriate to its setting. On the western wall, a large slab of mica schist, measuring 2.3 metres by 1.5 metres, carries an incised Latin cross. Robert Cochrane documented the structure in his detailed survey published in 1925 as part of the Eightieth Annual Report of the Commissioners of Public Works, and Harold Leask discussed it further in 1950.

The Discovery Programme has produced a 3D model of the gateway, which allows a closer study of its stonework and proportions than the site itself always permits, particularly useful given how much of the upper fabric is missing. A possible remnant of the enclosure wall runs from the north-eastern corner of the gatehouse, hinting at the larger boundary system of which this entrance was once just one carefully managed point.