It is barely a metre wide and not much more than half a metre high, built from drystone without mortar, and it runs underground through a circular cashel, the kind of stone-walled enclosure that once served as a fortified farmstead in early medieval Ireland. The depression where a visitor might pause to peer downwards was caused by the collapse or removal of one or two of the flat roofing slabs that once sealed the passage from above. What lies beneath is now inaccessible, but the exposed section of drystone walling is visible from the northern edge of the hollow.

The site at Lios Na Caolbhuí sits on fairly level pastureland with Brandon Bay visible to the east. The cashel itself encloses three hut-sites alongside the souterrain, a type of artificial underground passage commonly associated with early Irish settlement, likely used for storage or as a refuge. What makes this particular souterrain of additional interest is its apparent orientation: the passage seems to run towards the lintelled entrance through the cashel wall, suggesting a deliberate relationship between the two structures, though whether they were directly connected or simply aligned remains unclear. J. Cuppage, whose 1986 archaeological survey of the Dingle Peninsula first documented the site in detail, recorded these features without resolving that question, and it appears to have remained open since.