That combination of the knowable and the unresolved is characteristic of the souterrain, a type of underground stone-built structure found across early medieval Ireland. Typically associated with ringfort settlements, souterrains were constructed from drystone walling roofed with large flat lintels, creating chambers and crawl-ways that could serve as storage spaces, places of refuge, or both. This one, overlooking the valley of the River Inny in south-west Kerry, is a quietly compelling example of a form of building that was never meant to be seen.

The entrance, just one metre wide and less than a metre high, faces south and leads into a chamber whose walls are drystone and whose ceiling is formed by stone lintels laid across the top. From that first chamber the passage runs approximately 2.2 metres northward before bending to the north-east, where it continues for roughly another three metres. Beyond that point it proved inaccessible to those who surveyed it, though it was observed to carry on in a broadly northerly direction. How far it extends, and what it connects to, remains an open question. The structure sits on rough grazing land on a slope, unremarkable from any distance, with no obvious surface feature to signal what lies beneath.