It is claimed that the Heapstown Cairn, in Castlebaldwin County Sligo, is the largest cairn in Ireland outside of the Boyne Valley. It is 60 metres in diameter and almost 6 metres high, with a kerb of large limestone slabs enclosing the base.

Heapstown has not been excavated, but it is thought to most likely be a passage tomb, and extension of the Carrowhell megalithic complex.

At one time it was much larger but cartloads of the cairn were removed to build roads and walls during the last century. A drawing of the cairn by George Petrie in 1837 shows the presence of a large pillar stone at its summit and also indicated that there was much greater volume of stone.