A souterrain, in the simplest terms, is a man-made underground passage or chamber built in drystone or rock-cut technique, typically associated with early medieval settlement in Ireland, and often thought to have served as a place of storage, refuge, or both. This one was hidden so completely that the ground above it now shows no surface trace at all, and the construction work that accidentally exposed it also disturbed much of the surrounding archaeology.

When the structure was examined and described in 1980, it comprised a main chamber running roughly east to west, measuring around 4.5 metres in length, 1.9 metres wide, and rising to somewhere between 1.4 and 2 metres in height. The walls are of drystone construction, with large boulders forming the lowest course and smaller stones above, and there is some irregular corbelling where the upper courses meet the roof, which is formed by large stone lintels laid flat across the top of the walls. Off the eastern end of the main chamber, a low lintelled creepway, narrow enough to require crawling, leads north into a smaller, irregular chamber measuring roughly 1.5 by 1.1 metres. A recess in its north-west corner, combined with a large slab beneath it, may represent the original entrance to the whole structure. The current way in is an undignified slump through a gap where one lintel has been removed, and the floor of the main chamber holds animal bones of unknown date alongside scattered earth and stone. Traces of charcoal and burnt soil add a further layer of ambiguity, their origin and meaning unresolved. About 170 metres to the north-west of the site lies Loughazon Hall, formerly known as Mount Dalton House, which places the souterrain within a landscape that has been farmed and modified across many centuries. What connection, if any, the underground chambers have to the people who once worked or lived in that wider landscape remains, for now, an open question.