It is a bullaun stone, a type of ancient carved or worn rock bearing one or more cup-shaped hollows, found widely across Ireland and typically associated with early Christian sites or pre-Christian ritual use. What makes the Lissenhall example unusual is the density of functions local tradition has attached to it: a vessel for holy water, a cure for warts, and a clandestine altar.

The stone itself is a substantial piece of work, roughly a metre across in both directions and rising to 0.78 metres at its highest western edge, since its surface slopes upward from east to west. The principal hollow, located off-centre near the western edge, measures 0.27 metres across at the top and drops 0.14 metres deep; nine smooth water-rolled stones have been placed inside it, a practice sometimes associated with devotional rounds or votive offerings at Irish sacred sites. Two shallower depressions survive near the eastern edge. By the time an Irish Tourist Association survey was conducted in the 1940s, local knowledge identified the stone as the Ballycahill Mass Rock, a name pointing to its use during the Penal Laws, the period roughly spanning the late seventeenth and eighteenth centuries when Catholic worship was suppressed in Ireland and Mass was sometimes celebrated outdoors at improvised stone altars. The surveyor found it beside an old whitethorn bush on the rim of a semicircular depression in the ground, described as a roughly built table of large stones. Folklore gathered from Lissenhall school in the 1930s adds another dimension: children recorded that water collecting in the stone's hollows was used to cure warts, the depressions being known locally as wart wells, and that the same hollows had served as holy water fonts during Mass in Penal times.

The stone sits in grassland on an east-west ridge with open views across the surrounding countryside, the ruins of Lissenhall House visible about 100 metres to the south. Within a few hundred metres to the north-east lie two further water-related sites: a spring known as the Vaulted Well and, slightly further on, Patrick's Well, a holy well. The clustering of these features, bullaun, holy well, and mass rock tradition, in a compact upland area suggests that this was once a locality with a sustained sacred or communal character, even if that character is now mostly legible only through the landscape and the stones themselves.