What remains is a souterrain, an underground or semi-underground tunnel built from dry-laid stone without mortar, of the kind that early medieval Irish farmsteads used for storage, refuge, or both. This one survives in a state that is partly ruin and partly puzzle.

The site is known as Lisnagrave, or Lios na gCraobh in Irish, and it sits on level pastureland at the highest point of a low, gentle rise running east to west. The earthwork enclosing it is a univallate rath, meaning a roughly circular enclosure defined by a single bank and ditch, the most common form of Early Christian period settlement in Ireland. The souterrain lies in the south-western part of the rath's interior. Its passage runs just over three and a half metres from north-north-west to south-south-east, is barely a metre wide and only sixty-five centimetres high, so crawling would have been unavoidable. The walls are slightly corbelled, meaning each course of stone projects inward a little over the one below, and both the northern and southern walls curve gently rather than running dead straight. Only a single roofing slab remains in place. More intriguingly, the southern half of the eastern wall has collapsed, and the rubble that has accumulated there may be concealing the entrance to a second passage or chamber. Whether that debris hides something further, or simply marks where a wall gave way, remains unresolved.