What looks like an ordinary stretch of rough pasture is in fact the remnant of a concentric enclosure, two rings set one inside the other, separated by a gap of 72 metres. Most of it is invisible to anyone walking the ground. It was an aerial photograph, Air Corps image V. 312 3078/7, that first revealed the full extent of the site, showing the inner and outer circuits as cropmarks, those tell-tale variations in vegetation that appear above buried earthworks when soil moisture differs from the surrounding ground.

The two enclosures are dramatically different in scale. The inner ring measures roughly 50 metres in diameter; the outer stretches to approximately 180 metres across, making it a substantial feature by any measure. Concentric enclosures of this type are relatively uncommon in the Irish archaeological record and are thought in many cases to represent high-status settlements, where the outer ring may have enclosed agricultural activity or livestock while the inner defined a more protected living space. At Garryduff, the outer enclosure survives in the north-east quadrant as a broad, low bank, around 6 metres wide and only about 26 centimetres high on its external face, barely registering as a rise in the pasture. The inner enclosure has fared slightly better in places, largely because a later field boundary was built directly on top of it, incorporating the older earthwork into an earth and stone wall that stands over a metre high externally. A shallow ditch, 3.5 metres wide and 35 centimetres deep, accompanies the inner bank along its northern side. Elsewhere, the north-west quadrant of both rings survives only as a cropmark, the physical bank long since levelled.