It is roughly D-shaped, flat-topped, and measures about two and a half metres across, with a cross-shaped stone slab set upright at its centre. Modest in scale and easy to overlook, it marks a site where Catholic worship once had to be conducted in secret, far from official scrutiny.

The Penal Laws, which from the late seventeenth century severely restricted Catholic religious practice in Ireland, drove Mass outdoors to remote locations. These makeshift outdoor sites, sometimes called Mass rocks, were typically natural features adapted for liturgical use, a flat boulder serving as an altar, a hillside hollow providing shelter and concealment. When O'Kelly recorded this particular site in 1942, he described an older arrangement: a heap of stones and a large stone with a natural hollow that collected rainwater, which people used to bless themselves. Neither feature survives. At some point the original material was lost or dispersed, and in the 1960s local people built the current structure on the same spot, a deliberate act of commemoration using drystone construction, the traditional technique of stacking unmortared stone that is common across the west of Ireland.