It measures roughly 1.8 metres east to west and 1.5 metres north to south, rising about 0.8 metres from the ground. Locally, it is known as a mass-rock, and that name carries considerable weight. During the Penal Laws of the late seventeenth and eighteenth centuries, when Catholic worship was suppressed under British legislation, priests celebrated Mass outdoors and in secret, often at remote elevated sites where a lookout could watch the approaches. A flat rock in open hill country was an altar by necessity, and hundreds of such sites survive across Ireland, each one a marker of a period when the practice of a faith had to be conducted out of sight.

Two smaller slabs lean to the east of the main rock and may represent the remnants of a modest animal shelter, though nothing about them is certain. What gives this particular spot an additional layer of interest is its proximity to the old Butter Path, an ancient routeway that runs along the lower slopes of Shehy Beg, roughly 70 metres to the north. Butter roads were the working arteries of pre-Famine rural Ireland, the tracks along which farmers drove their produce, usually in wooden firkins, to market towns and coastal ports. That a clandestine place of worship should sit so close to one of these everyday routes is quietly telling: the congregation would not have needed to make a special journey into the wilderness. They were already passing through.