The cairn itself is substantial, some thirty metres across and up to three and a half metres high, and whoever cleared its centre did so with enough thoroughness to leave foundations and a functioning well within what had once been solid mounded stone.

The cairn's origins remain genuinely uncertain. Michael Herity, writing in 1974, proposed that it may be a passage tomb, the type of Neolithic monument in which a stone-lined corridor leads to a burial chamber beneath a large cairn, most famously seen at sites like Newgrange. But the usual diagnostic feature of such tombs, a kerb of upright stones ringing the base, is entirely absent here. Three slabs survive in the south-western quadrant, though whether these are remnants of an inner structure or simply displaced stones is not clear. What is certain is that at some later point, probably in the early medieval period when the practice of building small churches on elevated or already-sacred sites was common across Ireland, the mound's centre was deliberately hollowed to create an enclosure. Within that enclosure, a church was built and a well established, both now reduced to foundations and surviving masonry. The mountain's name, Church Mountain, is in all likelihood a direct reference to this building rather than to any later ecclesiastical use of the hill.