Eleven metres long, five metres wide, and roughly a metre deep, the sunken outline marks the collapse of a souterrain, an artificially built underground passage or chamber, typically dry-stone lined and roofed with large flat slabs, used in early medieval Ireland for storage, refuge, or both. The two stone-roofed chambers it once contained are long gone.

The souterrain sits in the western quadrant of a ringfort on level ground that falls gently to the east, south, and west before rising to the north, with broad views across a plain in both directions. The field enclosing it carries the name Bawnacrusha, a townland name likely derived from the Irish for a settlement enclosure. The local historian William Carrigan, writing in 1905 in his four-volume history of the Diocese of Ossory, noted the monument as a partially dismantled rath in which two stone-roofed apartments had been discovered, though already destroyed by his time. Carrigan mistakenly placed the site in the neighbouring townland of Butlerswood rather than Garryrickin, a small geographical error that may have contributed to the souterrain receiving less attention than it might otherwise have done. What he described as apartments were almost certainly the two chambers of the souterrain, their roofing slabs presumably removed or fallen in during the centuries before he visited.