A semicircular platform, roughly 28 metres north to south and 18 metres east to west, sits quietly beneath the grass, its eastern edge defined by a field boundary running north-east to south-west. It takes an aeroplane, and the right quality of light, to make it appear at all.

The enclosure came to light through a single aerial photograph taken in 1978, catalogued under reference BKS 2776139/40. Aerial survey of this kind works by detecting cropmarks or soilmarks, subtle variations in vegetation or earth colour that betray buried or levelled features below the surface. Enclosures of this general type, roughly circular or semicircular platforms sometimes associated with early settlement or agricultural activity, are not uncommon across the Irish uplands, though many remain unexcavated and undated. This one was compiled for the record by archaeologists Geraldine Stout and Padraig Clancy, with a revised upload noted in July 2018, suggesting it remains part of an ongoing effort to document features that might otherwise slip entirely from notice.

Three Rock Mountain is accessible from several points on its lower slopes, and the general area around Woodside is open upland ground. Because the enclosure is not visible at ground level, there is nothing to see in the conventional sense, no earthwork to trace with your foot, no raised bank to walk around. What makes a visit worthwhile is more a question of orientation: standing in the approximate area and knowing that the shape exists, recorded once in a photograph from forty-odd years ago, somewhere beneath the ordinary-looking pasture. The mountain itself offers good visibility back towards the city, and the field boundaries in this part of the slope are themselves worth attention, since one of them is apparently all that now marks the eastern edge of the feature.