The souterrain, a type of underground stone-lined passage or chamber built during the early medieval period and associated in Ireland with ringforts and farmsteads, was closed up in the modern era. What remains accessible to the eye is a shallow, stony depression, roughly 5.3 metres east to west and 2.2 metres north to south, tracing the line of what lies below.

The structure itself, as recorded from local information, consists of a short stone-lined entrance leading into a roughly square chamber, approximately 1.8 metres on each side and about 1.2 metres high, not quite enough headroom to stand upright. Off that chamber, there is an opening into a further passage, though that too is now blocked. Souterrains of this kind are found across Ireland in considerable numbers, often interpreted as storage spaces or places of refuge connected to the enclosures, known as raths or ringforts, that were the typical farmsteads of early medieval Ireland. The rath at Laralae provides that context here, the souterrain sitting within its boundary rather than as an isolated feature. The depression visible at the surface, running along a raised ridge through the rath's interior, is likely all that now marks its presence above ground.