What makes the place quietly unsettling is not simply its age but the condition it was left in after a round of well-intentioned clearance work in 2010. During efforts to tame the overgrown site, stonework loosened by ivy removal was taken down rather than conserved. At least four courses of the western gable and the upper stones of the northern wall were removed entirely, with the displaced stone piled inside the church along with a number of architectural fragments. When tree growth within the interior was dug out, skeletal material was exposed, a reminder that the ground here had been used for burial over a long period.

The church is dedicated to St Marnock, an early Irish saint, and its history as an organised religious site stretches back at least to 1172, when it was granted to St Mary's Abbey in Dublin. By the mid-seventeenth century it had already fallen out of use as a functioning church. Both the Down Survey of 1655 to 1656 and the Civil Survey of 1654 to 1656 record it, the latter describing it simply as 'Chapell walls', suggesting the structure was already ruinous by that point. The building itself is a long rectangular form constructed from roughly coursed limestone, with dressed stone quoins, the carefully shaped corner stones that give a medieval wall its structural stability, visible on the west gable. It has an undivided nave and chancel, meaning there is no internal division between the two sections that would typically be separated in a more elaborate church. Inside the chancel, which is now closed off by an iron gate, a piscina survives with a damaged round-headed arch; a piscina is a shallow stone basin used for washing communion vessels, and its presence here is a small but telling detail about the liturgical life the building once held.

The site is accessible from the Velvet Strand area, off the main coast road. The west gable retains a square-headed window set under a segmental arch, and the ghost of a former bellcote can be read in the stonework above it. Windows in the south wall of the chancel and in the east gable have been blocked up. The iron gate across the chancel prevents entry to that section, but the nave remains open to view. Given what was disturbed during the 2010 work, it is worth approaching the interior carefully and being aware that the ground underfoot may not be as undisturbed as it appears.