It measures roughly two metres east to west and one and a half metres north to south, its stones partially collapsed and now almost entirely submerged beneath the rising waters of the lake. It is the kind of thing you could wade past without a second thought, yet it has attracted curiosity, confusion, and disagreement for over 150 years.

The first person to describe it in print was Kinahan, who in 1872 identified it as the ruin of a fosleac, an Irish term for a type of flagstone-covered burial monument. Lord Killanin, writing in 1954, was less certain, suggesting it might simply be natural. The structure had already been marked on the Ordnance Survey six-inch map of 1838, noted by name only as 'Carn' on the verge of an old roadway running along the southern lakeshore. The area immediately to the south was recorded on that same mapping as 'Laghta', a placename that itself carries associations with burial or memorial sites in Irish. By November 1983, when the site was formally inspected, no visible surface trace could be found at all. Then, in 2022, it was relocated by M. Gibbons, who photographed what remains: a low, roughly rectangular heap of stone, mostly swallowed by the lough.

What makes this place quietly unsettling is not any one dramatic fact but the accumulation of uncertainty around it. A name on a nineteenth-century map, a disagreement about whether it was ever man-made, a decades-long disappearance from the record, and now a gradual, ongoing submersion. Whether the rising water level is a long-term change or a seasonal fluctuation, the cairn seems to be going under for good.