What it revealed was a cist, a small box-shaped burial chamber built from stone slabs, of a type associated with prehistoric funerary practice in Ireland. These structures were typically constructed to hold a single crouched burial, sometimes accompanied by grave goods, and were then covered with a capstone and buried beneath the earth. This one had been waiting on a pronounced natural knoll, on a terrace overlooking a quiet river valley, the river itself running some seventy metres to the east before joining the Pil River to the south.

The cist at Bregaun is modest in its dimensions, roughly rectangular, measuring between 0.4 and 0.55 metres in length, 0.37 to 0.5 metres in width, and just over 0.31 to 0.34 metres in depth, with its long axis oriented northwest to southeast. Each of the four sides is formed from a single slab of stone set on edge, with a slender upright stone filling a small gap in the southern corner. Most of the slabs are conglomerate, a sedimentary rock formed from cemented fragments of older stone, though the northeast side appears to be slate, suggesting the builders used whatever suitable material was available locally. At the southeast end and southern corner, two thin stones project slightly beyond the edge of the structure, almost certainly the supports for a capstone that once roofed the chamber. That capstone, and any other evidence of the former cover, is now entirely gone. Whether the knoll on which the cist sits is purely natural or was built up deliberately to give the burial a more elevated position remains an open question.