Scattered at its southern end are several large stone slabs that may once have formed part of a roof. The working theory is that what you are looking at is the collapsed remains of a souterrain, an underground passage or chamber, typically stone-lined and roofed with flat lintels, that was constructed in early medieval Ireland for storage, refuge, or ventilation of perishable goods.

The souterrain sits within a rath, which is the Irish term for a roughly circular earthwork enclosure, usually defined by one or more banks and ditches, that served as a farmstead during the early medieval period, broadly from the fifth to the twelfth century. Raths are among the most common archaeological monuments in Ireland, and souterrains are frequently found within them, though the combination is never entirely routine. Here at Kilmore, the detail comes from local knowledge rather than excavation, which means the identification of the depression as a souterrain remains probable rather than confirmed. The displaced lintels at the southern end are the most suggestive physical evidence, hinting at a chamber whose roof has given way over time, leaving the long shallow hollow now visible at the surface.