The entrance is still visible, a stone-lined opening that slopes downward from the north-western quadrant of the fort, and to the east of it two sunken hollows in the ground hint that further chambers once extended underground before the earth above them gave way.

The structure is a souterrain, a type of deliberately constructed underground passage or chamber found throughout early medieval Ireland, typically built from dry-stone walling and roofed with large flat lintels. Their precise function is still debated, though they are generally thought to have served as cold storage, refuges, or both. This particular example sits at the centre of the ringfort, which is itself a common arrangement; souterrains are frequently found within ringforts, the enclosed farmsteads of early medieval Ireland. The passage here reaches a recorded height of around 1.1 metres, low enough that anyone moving through it would have had to crouch, and a short creepway leads into the stone-lined section before the route turns at a right angle and meets the collapse that now defines its limit.