It is the only surface trace of a souterrain, an underground stone-lined passage or chamber typically built during the early medieval period in Ireland, often for storage or refuge. The site does not appear on Ordnance Survey maps, and the passage itself has been blocked and inaccessible for years. There is nothing to announce it.

Locally, the hillock goes by the name Cnocán na hÓnach, recorded by Ó Cíobháin in 1984. The souterrain's passage is oriented east to west, a detail that survives in the record even as the physical entrance has long since closed over. The strand nearby is known officially as the White Strand but is called Glanbeg Strand locally, a name that echoes the Irish An Gleann Beag, meaning the small glen. The combination of a local place-name preserved in oral tradition, a slab slowly disappearing into grass and scrub, and an underground passage that nobody living has entered gives the site a particular quality: it is a presence defined almost entirely by absence.