It measures barely 35 centimetres in height and 80 centimetres across, sealed by a limestone lintel slab, and whatever passage once extended beyond it is now blocked with earth. This is a souterrain, an underground stone-lined tunnel typically constructed during the early medieval period in Ireland, used variously for storage, refuge, or concealment. That the entrance survives at all, however modest, gives the site a quiet coherence.

The souterrain sits on the western side of the interior of Lisduff rath, positioned at the northern base of a roughly rectangular, flat-topped mound standing about 1.2 metres high. A rath, sometimes called a ringfort, is an enclosed farmstead of the early medieval period, defined by one or more circular earthen banks. Souterrains were frequently incorporated into such enclosures, often opening from the interior bank, as this one does, placing the underground access point within the most protected part of the site. The mound itself is modest in scale, its top surface running just over two metres north to south and slightly wider at its base, suggesting the accumulated material of both deliberate construction and centuries of settling. The limestone lintel speaks to the care taken in the original build, even if the passage behind it is no longer accessible.