O'Brennan, the parish name attached to this graveyard in the townland of Crag, County Kerry, does not refer to a family. It derives from the Irish Uaimh Bhreannán, meaning Brendan's Cave, and that cave, or rather its absence, is what gives the site its quietly unsettling character. A place of early Christian significance, remembered in ecclesiastical Latin as Antro Sancti Brandani, the cave of St Brendan, it was once preserved, according to the Reverend Denis O'Donoghue writing in his 1893 work Brendaniana, with religious care through many centuries, with a small nunnery maintained close beside it. By the time O'Donoghue was writing, the convent had left no trace and the cave itself could no longer be identified with certainty. He attributed the destruction to a stone-robber who had quarried into it some decades earlier, destroying almost every vestige of it.

The cave's association with St Brendan, patron saint of Kerry, reaches back to a tradition recorded in local scholarship: that in 494 AD the ten-year-old Brendan was sent by his foster-father, St Erc, to spend a night in the cave as a penance for some unnamed misdemeanour. Whether or not the story is historical, it was clearly compelling enough to anchor a parish around the site for over a millennium. By 1302, when the papal taxation of the Diocese of Ardfert valued the Church of St Brandan's Cave at ten shillings per annum, the cave had already lent its name to a functioning ecclesiastical structure. Church records through the fifteenth and early sixteenth centuries continue to refer to it by its Latin cave-name: Geraldus Stack is noted as cleric of the parish in 1493, Nicholas Ohuran as presbyter in 1494, and in 1517 tithes were collected from the church by Mauritius Oconcuor of Ardfert. By 1368 the rector was one John de Geraldines. The Royal Visitation of 1615 still listed it as the Rectory of Brenan, but by 1756 Charles Smith was recording the church as already in ruins, and when the scholar John O'Donovan visited in July 1841, he found no remains of the church at all.

What survives today is ambiguous in the most literal sense. The graveyard remains active and well used. A 2010 survey by Laurence Dunne identified the low outline of what may be a rectangular structure on a raised platform amid the tombs, aligned east to west in the manner of a medieval church, though overgrown with grass and briars and too unstable to examine closely. In the north-east corner of the graveyard, a pronounced depression in the ground may mark the site of the cave itself. Nothing is certain. The name of the place, and the hollow in the earth, are what remain of a story that begins with a child sent into the dark as punishment, and ends with a quarryman who wanted the stones.