The feature is small, roughly one and a half metres long and half a metre wide, defined on three sides by upright stones and set into the south-western corner of the enclosure. What it represents, most likely, is the entrance to a souterrain, one of the underground stone-lined passages that were constructed across early medieval Ireland, typically as places of refuge, storage, or concealment.

Raths, also known as ringforts, were the farmsteads of early medieval Ireland, enclosed by one or more earthen banks and ditches. Souterrains were a common feature within them, though they vary considerably in scale and complexity, from short single chambers to elaborate tunnel networks. The one at Lisbabe is tentatively identified rather than confirmed, the language used to describe it deliberately cautious. The stone slabs define only three sides, leaving the fourth open, and what lies beyond that opening, if anything does, has not been fully investigated. The rath itself is a separate recorded monument, suggesting the two features are understood as related parts of the same early medieval landscape.