A section of its roof has collapsed, and it is through that collapse that anyone curious enough can now enter. Before that happened, the only way in or out would have been whatever deliberate opening its builders intended, and that opening is now lost.

The structure is a souterrain, an underground passage or chamber built by drystone construction, meaning the walls are assembled from carefully fitted stones without mortar. Souterrains are found across early medieval Ireland, typically associated with raths, the circular earthwork enclosures that served as farmsteads from roughly the sixth to the twelfth centuries. Their precise function is debated, with storage of food and dairy produce, refuge, and ventilation all proposed at various points. This one sits within the north-eastern quadrant of just such a rath and was built to a rectangular plan, running on a north-east to south-west axis. The surviving passage measures around four metres in length, roughly one and a half metres wide, and reaches a maximum height of just under one and a half metres, meaning movement inside would have required a low crouch. The total confirmed length exceeds ten metres, but the more telling detail lies beyond the current point of access: a linear depression in the ground, six metres long and nearly three metres wide, traces the likely continuation of the passage further to the south-west, suggesting that what remains visible today is only part of what was once built.