This circular fortification, measuring approximately 30 yards in diameter, featured a defensive parapet constructed from clay and stone. What made this site particularly fascinating was the extensive cave system, or souterrain, hidden beneath the fort's surface.

The underground passage that Fagan explored stretched for at least 30 feet, with the visible section varying between 3 to 5 feet in width and a rather cramped 2 to 3 feet in height. These souterrains are characteristic features of Irish archaeology, typically dating from the early medieval period; they served various purposes including storage, refuge during raids, and possibly ritual activities. The combination of an above-ground fort with an elaborate underground system suggests this was once a significant defensive site, likely belonging to a local chieftain or important family.

Despite its detailed documentation in Book 19 of Fagan's records, modern archaeological surveys have been unable to relocate this site. The fort and its subterranean passages have seemingly been reclaimed by the landscape, lost amongst the rough grazing lands that now characterise the area. This disappearance isn't uncommon in Irish archaeology; many earthwork sites have been gradually levelled by centuries of agricultural activity, leaving only historical records as evidence of their existence. The site was catalogued as DG097-010001 in the Archaeological Survey of County Donegal, compiled by Brian Lacey and his team in 1983, ensuring that even though the physical remains have vanished, the memory of this mysterious fort and its hidden depths remains preserved.