The opening measures roughly sixty centimetres high and one and a half metres wide, and it leads into a souterrain, an underground stone-lined passage of the kind built throughout early medieval Ireland, typically for storage, refuge, or both. What makes this one quietly notable is that it does not appear on Ordnance Survey mapping at all, meaning it has slipped through the usual documentary record that most archaeological sites in Ireland leave behind.

The structure itself is dry-stone built, meaning the walls were raised without mortar, the stones carefully chosen and stacked so that the walls taper inward to meet a roof of large horizontal lintels. This corbelling technique was common in souterrain construction and could produce surprisingly robust underground chambers. At the southern side of the enclosure bank, the earthwork has been disturbed, and a large lintel can be seen pushing out from the bank, hinting at the scale of the stonework concealed within. The souterrain sits in the southern quadrant of the enclosure associated with Creeve Castle, placing it within a landscape that was clearly used and reorganised over a long period, though the precise relationship between the underground passage and the later castle above ground is not recorded.

The site occupies a rise with open views across the surrounding countryside, though the souterrain entrance itself is now largely obscured by scrub vegetation, making it difficult to see clearly from above even on aerial photography. The bank disturbance and the projecting lintel remain the most visible indicators of what lies beneath.