The entrance is now closed up, and what lies beyond it remains, in practical terms, unknown. That incompleteness is part of what makes it interesting: a structure built to be entered, quietly resisting the effort ever since.

Souterrains are stone-lined underground passages or chambers, typically associated with early medieval ringforts in Ireland, and thought to have served as refuges, storage spaces, or escape routes. The one at Ballycunningham was investigated in 1939 by P. J. Hartnett, who found a passage just two feet wide, its walls built of stone and its ceiling formed from flat stone lintels laid across the top. He could only push a short distance in before being stopped, but he noted that surface disturbances in the ground suggested the passage continued for around twenty feet, running eastward toward the centre of the fort. Whether it opened into a chamber at that end, or simply terminated in the earth, he could not say.