The earthwork above them is a ringfort, the circular enclosure type that dots the Irish countryside in the thousands and dates broadly to the early medieval period. This one, sitting on gently rolling farmland with open views across tillage and pasture in all directions, carries the local name Raavloughlan's fort. Beneath its western interior lies what is known as a souterrain, an underground stone-built passage or set of chambers associated with ringforts, most likely used for storage or refuge. What makes this one quietly remarkable is the quality of the construction that was recorded before it was lost to view.

When Healy investigated the site in the late nineteenth century, he found three chambers arranged in a direct line, the largest measuring roughly 3.45 metres by 2.1 metres, with a floor nearly 4.2 metres below the surface. The doorways connecting the rooms were barely 76 centimetres high and just 41 centimetres wide, with inclined jambs on the passage between the first and second chambers. The building material, limestone and a whitish gritstone, had been quarried within a hundred yards of the fort itself, the two quarry sources still identifiable nearby. Healy noted that the third chamber had a door on its north side leading nowhere, as though further passages had been planned but never completed. He also recorded that some eighty years before his visit, men from Kilkenny digging in search of gold had broken through the roof of that third chamber. Carrigan, writing in 1905, confirmed the fort's reputation for its underground chambers. Healy himself had constructed a rough staircase to help visitors descend without crawling. The souterrain has since been backfilled, though one chamber with the remains of its corbelled roof, a technique in which stone courses are stepped inward to form a ceiling without any central support, remains partially visible at the surface.