The passage is a souterrain, a type of underground or semi-underground stone-lined tunnel found at many early medieval Irish sites, often used for storage or refuge. This one, however, was purpose-built for escape.

Cahercommaun is a triple-walled cashel, a dry-stone ringfort, set on a promontory above a steep limestone ravine in the Burren. When Harvard archaeologist Hugh Hencken excavated the site in 1938, he identified the souterrain as connecting the dwelling of what he called the 'chief occupant' directly to the cliff edge, via a crevice in the rock face below. The tunnel measures seven metres in length and between 0.67 and 1.1 metres in width, narrow enough to require some determination to move through quickly. On the bedrock at the bottom, excavators found a layer of ash mixed with bones, roughly 35 centimetres deep, the nature of which raises more questions than it answers. Whether those deposits relate to routine domestic disposal or to something more charged is not recorded, but the combination of a hidden exit, a cliff drop, and burned material at the base gives the place an atmosphere that numbers alone do not quite capture. Cahercommaun is a national monument in State care, and the souterrain sits within its northern portion, associated with the innermost and most protected area of the fort.