The souterrain, an underground stone-built structure of the kind typically associated with early medieval ringforts, where they served as storage spaces or places of refuge, sat undisturbed in the north-eastern quadrant of a ringfort until the fort itself was levelled. That act of demolition, which erased one layer of archaeology entirely, inadvertently exposed another.

The site was investigated by Walsh and by the archaeologist M. J. O'Kelly, who recorded two chambers connected by a narrow creepway. The first chamber, oriented north to south, measures roughly 2.4 metres in length, a metre wide, and a metre high. Its walls are corbelled, meaning the stones are laid so that each course projects slightly inward over the one below, and the chamber is roofed with flat lintels. Access today is only possible through a section of collapsed roof. A narrow creepway on the eastern side of the chamber's northern end, just 27 centimetres wide and 50 centimetres high, connects to a second chamber running east to west, though this second space has also collapsed and is now inaccessible. What makes the structure particularly intriguing is one of the lintels in the first chamber. On its downward-facing surface, O'Kelly noted a polished area bearing a group of pin-grooves. Such markings are not fully understood, but their deliberate, repeated character suggests use rather than accident, possibly connected to craft activity or something more ritual in nature. There is now no surface trace of any of this.