A shallow linear depression, roughly five metres long and no more than two metres wide, traces the roof line of an underground passage that has been there far longer than anyone walking the field today. Where one of its capstones has shifted out of place, a gap opens into a low drystone-walled corridor, barely a metre wide and less than a metre high, still largely intact beneath the surface.

A souterrain is an artificially constructed underground passage or chamber, typically built during the early medieval period in Ireland and used for storage, refuge, or both. This one sits on top of a north-to-south ridge, close to where the ground falls away on the western side, a position that would have made practical sense for drainage as much as concealment. Three of the original roofing lintels remain in place; a fourth has slipped, creating the cavity that now offers the only glimpse inside. The structure was entirely absent from the Ordnance Survey's six-inch map of 1837, which suggests it was either buried and forgotten by then, or simply missed. By the 1930 edition, it had reappeared, marked with the straightforward label "Cave", which is the kind of cartographic understatement that tells you a surveyor knew something was there but was not entirely sure what to make of it.