A souterrain is an underground stone-built passage or chamber, typically associated with early medieval ringforts, and used variously for storage, refuge, or both. This one is unusually well preserved for all that its parent ringfort, a rath, has been poorly maintained above ground. The rath itself, a type of enclosed farmstead defined by earthen banks, is now hard to make out in the meadowland, but the subterranean structure beneath it remains largely intact.

The construction is drystone throughout, meaning no mortar was used, relying instead on the careful fitting of stone against stone. The accessible northern chamber stretches roughly 4.6 metres east to west, its slightly rounded ends giving it a subrectangular form. Massive roof lintels cap the space, with the wider gaps between them bridged by smaller cross-flags, a practical solution to spanning an irregular ceiling without cutting stone to fit. Where the clay floor is visible at the western end, there is a headroom of 1.6 metres. Two small niches are cut into the gable ends, one at floor level to the east and a slightly larger one set a little higher to the west, their function now uncertain but possibly used for lamps or small stored goods. Two air vents punctuate the northern wall just below the corbelled course that carries the roof, a detail that suggests this was a space intended for more than short-term use. The southern chamber mirrors the northern one in apparent size and construction but is no longer accessible; a small opening allows only a limited view inside. Entry to the northern chamber is through a lintelled ope, a doorway formed by a horizontal stone laid across upright supports, measuring 0.7 metres wide and 1.4 metres high, reached via a short connecting passage whose roofstone has been removed.