It measures just thirty centimetres high and fifty-five centimetres wide, the entrance to an L-shaped underground passage built without mortar from carefully fitted stones. This is a souterrain, an artificial underground chamber or tunnel of the early medieval period in Ireland, typically associated with nearby settlement and thought to have served for storage, refuge, or both. That such a structure survives at all here is quietly remarkable; what draws attention is less the engineering than the setting, poised between St Finan's Bay to the west and Ballinskelligs Bay to the east, with open views in both directions.

The souterrain belongs to a small cluster of remains on this slight terrace at An Com. A pair of conjoined huts, roughly square in plan and now poorly preserved and heavily overgrown, stand nearby; some upright slabs still form part of the inner wall-face of the northern hut, which measures about 2.3 metres across and stands to a height of around 0.9 metres. The underground passage itself runs westward from the hut complex for 1.6 metres, then bends southward through a low creepway, where collapsed material prevents any further exploration. The structure is drystone-built throughout, its passage lined and roofed with flat stones. This kind of corbelled and lintelled underground architecture is found widely across early medieval Ireland, but examples on the Iveragh Peninsula are particularly associated with the dense concentration of early Christian and pre-Norman settlement that characterises this stretch of the Kerry coast. The site was documented by A. O'Sullivan and J. Sheehan in their 1996 archaeological survey of the peninsula, published by Cork University Press.