It is a souterrain, a type of underground stone-lined passage or room constructed, typically in the early medieval period, for purposes that still prompt debate among archaeologists: cold storage, refuge, ritual use, or some combination of all three. This particular example is now so heavily infilled with accumulated soil and debris that interpretation, as those who have examined it note, is genuinely difficult.

What can be measured gives some sense of the original space. The single chamber runs roughly north to south, stretching 2.6 metres in length, 2.9 metres in width, and standing just 1.1 metres high, a height that would have required anyone moving through it to crouch. It sits in isolation, with no obvious associated structures recorded nearby, which makes it harder to place within the usual pattern of souterrains found in connection with ringforts or early settlement enclosures. The record of it derives from a 1994 archaeological survey of the Ballinrobe district, covering the areas around Lough Mask and Lough Carra, a region whose landscape holds considerably more buried history than its surface tends to suggest.