The structure is a souterrain, an early medieval stone-lined tunnel, typically built without mortar, that was used for storage, refuge, or both. What makes this one quietly melancholy rather than simply ancient is the evidence of what has been done to it. By the time anyone looked carefully at it in 1980, a number of its lintels, the flat capstones laid across the passage to form a roof, had already been removed and broken up.

The souterrain runs from the inner bank of its enclosing rath, a type of circular earthwork enclosure common across Ireland from the early medieval period, extending in a westerly direction through the north-western quadrant of the site. When inspectors visited in 1980, some lintels were still lying in place, visible at the edge of a circular depression that had formed in the inner bank, suggesting a collapse or deliberate disturbance had opened up the ground above. A decade later, in 1990, the souterrain was recorded as entirely inaccessible, its condition having deteriorated further in the intervening years. The reference for that later assessment appears in Lavelle's 1994 survey of the region. What was once a hidden underground space, presumably sealed and dark for centuries, is now neither properly open nor properly intact.