This is a leacht, a type of commemorative cairn or rectangular stone structure associated with early Irish ecclesiastical sites, often used as a focus for devotional rituals. The example on St Macdara's Island, measuring roughly 2.7 metres east to west, is one of five recorded there, all of them gathered around the remains of a church near the island's south-eastern end.

When the antiquarian F.J. Bigger photographed this structure in 1896, it was still standing three to four courses of stone high. On top of it sat a cross-slab and what his account described as several spherical praying or cursing stones, smooth rounded boulders that feature in Irish devotional practice and, in some traditions, were believed to carry the power to call down harm when turned or used with intent. The leacht has since collapsed considerably. Today only two set stones remain visible on its western side and one on its southern side, with the interior reduced to scattered rubble. The cross-slab, once resting on top of the structure, has been moved and is now set into the ground about three metres to its north-north-west. Two of the rounded stones, one of limestone and one of granite, can still be seen on the western side, and a small granite boulder nearby may be another of the original cursing stones. A second cross may also be associated with this leacht, suggesting the site once carried more visible devotional apparatus than what survives now. The whole structure sits within an enclosure roughly twenty metres north-east of the church, part of a wider complex that marks St Macdara's Island as one of the more intact early Christian island sanctuaries on the western seaboard.