The first edition six-inch OS map labels it 'Carriggalla Fort', depicting it as a circular enclosure. By the revised 1927 edition, that name had quietly shifted to 'Carriganaffrin', an Irish place name meaning 'the Mass Rock'. The change is telling. Somewhere between those two surveys, the understanding of what this place was, and what it had meant to local people, had been folded into the cartography.

The site sits on elevated rocky ground with open views to the east, south, and west, and a clear sightline to the southern shoreline of Lough Gur some 300 metres to the north-west. What the maps recorded as a fort is thought to be the remains of a cashel, the Irish term for a stone-walled ringfort, which was later put to a very different use. During the Penal Laws, when Catholic worship was suppressed in Ireland, communities across the country gathered at outdoor 'mass rocks', unassuming stones or outcrops that served as improvised altars, often in remote locations where surveillance was less likely. This outcrop appears to have been one such place. A small cave-like recess on the south-west face of the rock may have sheltered the altar from the elements. The antiquarian Crofton Croker, writing in 1833, went further still, suggesting the fort had once been among the Royal forts of Ireland and identifying it with a site called Uillcan Eatan, a claim repeated by Barry in 1900, though it remains speculative.

The top of the rock is covered in scrub vegetation and is not accessible to visitors. There are no visible surface remains of any enclosing wall or bank around the base that would confirm the circular fort shown on the first edition map. The cave-like recess on the south-west face is the most tangible feature a visitor can observe from ground level. The site sits in good company: a church and graveyard lie roughly 280 metres to the north-west, and Ballynagallagh Nunnery is visible around 690 metres to the south-west. For those already exploring the Lough Gur landscape, this outcrop rewards a careful look, less for what can be seen than for the layered history compressed into a single, unremarkable-looking rock.