Known locally as the ‘Giant’s Bed’ on 19th-century Ordnance Survey maps, this trapezoidal stone mound stretches roughly 25 metres from northeast to southwest and rises modestly above the surrounding boggy ground. Though damaged by treasure hunters sometime before 1846, who dug a substantial pit at its northeastern end, the cairn has revealed remarkable secrets about Ireland’s prehistoric past.

Archaeological excavations in 2010 and 2011, conducted ahead of a planned dam construction, uncovered an oval stone mound measuring approximately 24 by 16 metres that contained two small chambers or cists at its southwestern end. The construction involved three distinct phases: first, a level foundation was laid incorporating the two cists; then this foundation was enclosed by a stone bank with large revetment stones at its base, defining an oval area; finally, angular stones filled the space to create the main body of the cairn. Radiocarbon dating of charcoal from one cist produced a Neolithic date of 3695-3535 BC, whilst numerous flint artefacts including scrapers, blades and flakes were recovered throughout the structure, likely lost or discarded by the cairn’s builders or early visitors.

The excavations revealed that this location served as a significant ceremonial focal point for nearly two millennia. Evidence of Neolithic hearths predating the cairn, an early Bronze Age wedge tomb built immediately to the southwest, middle Bronze Age burning pits and spreads, and a late Bronze Age fulacht fia just 6 metres north all demonstrate continuous use of this sacred landscape. Pollen analysis suggests that during the Neolithic period, this was an exposed upland plateau with open birch woodland and alder trees around the lake shore, before blanket bog began developing from the mid-Neolithic onwards. The cairn’s strategic position overlooking the Barnesmore Gap likely made it an important landmark along a prehistoric routeway, marking this spot as a place of enduring significance in Ireland’s ancient past.