The name, rendered variously as "The Cashel" and "The Cashell", adds to the slight confusion, since a cashel typically refers to a stone-walled early medieval enclosure, yet what survives here appears to be something considerably older.

The structure is believed to be a court-tomb, a type of megalithic monument built during the Neolithic period, generally thought to date from around 4000 BCE or earlier, in which a stone-lined forecourt opens into a roofed gallery used for communal burial. At Cornamucklagh, the cairn, the mound of stones that would originally have covered the tomb's chambers, measures roughly 29 metres along its north to south axis and about 18 metres wide, with a roughly trapezoidal shape. At its northern end is a deep U-shaped court, approximately 6.5 metres long and 3.6 metres wide. Of the gallery itself, only a single side stone survives. The monument occupies a slight col, a shallow saddle of ground between two local rises, with a summit of around 120 metres to the north and a higher one of approximately 340 metres to the south-east, a positioning that would not have been accidental to whoever chose it thousands of years ago.