The rock juts from an east-facing slope in rough hill pasture and arranges itself into three descending tiers, the largest at the top and each one stepping down and inward, reaching about 1.35 metres in height and spanning roughly 2.7 metres north to south. It is exactly the kind of feature that could pass unremarked, and for a long time that was precisely the point.

During the Penal Laws, the series of statutes enforced from the late seventeenth century onwards that banned Catholic worship, restricted Catholic land ownership, and effectively criminalised the priesthood, Mass could not be said openly. Congregations gathered instead at remote outdoor sites, often with a flat or elevated stone surface serving as the altar. Here in Derrylough, local tradition holds that the uppermost tier of this natural outcrop served as just such an altar, with the slope of the hill providing a natural amphitheatre of sorts for those assembled below. A second section of outcropping rock abuts the formation to the west, giving the site a slightly enclosed character. A footpath runs adjacent to the north side, which suggests the place was known and accessed regularly, even if its purpose had to remain discreet.

Mass rocks survive in considerable numbers across Ireland, particularly in areas like Kerry where the terrain offered both shelter and distance from centres of authority. What makes this example quietly affecting is its unaltered, unembellished state: rough hill pasture, natural stone, a worn path. Nothing here was built or improved. The landscape itself was the church.