The find came during the 1987 to 1988 excavation of Lisnagun ringfort, one of the earthen enclosures that dot the Irish countryside as remnants of early medieval settlement. What emerged was a souterrain, an earth-cut underground structure of the kind commonly built in Ireland between roughly the seventh and twelfth centuries, typically used for cool storage or as a refuge in times of danger.

The souterrain at Darrary consists of a barrel-vaulted chamber, meaning its ceiling curves upward in a continuous arch rather than sitting flat, cut directly into the earth rather than lined with stone. It measures four metres in length, 1.6 metres wide, and 1.4 metres high, compact enough to require stooping but substantial as an underground space. Running alongside it is an associated trench approximately 5.5 metres long, 1.2 metres wide, and 1.6 metres deep, which excavators interpreted as possibly the eroded remains of an entrance passage, a creepway, and a further chamber. A creepway is the deliberately low connecting tunnel between sections of a souterrain, designed so that anyone moving through it would have to slow down, giving defenders an advantage. The trench terminates at what may be an air vent, a detail communicated by J. O'Sullivan and one that hints at a more elaborate original structure than the collapsed remains alone would suggest. The souterrain was only partially excavated, so the full extent of what lies beneath the field at Darrary remains unknown.