It is a bullaun stone, a type of ancient hollow ground or pecked into rock or boulders, found widely across Ireland and typically associated with early Christian sites, holy wells, or places of ritual significance. The bowl here is notably deep relative to its width, measuring roughly 21 centimetres across but 22 centimetres deep, with smooth sides that suggest repeated use over a long period.

Bullauns are among the more enigmatic survivals of early medieval Ireland. Their precise function is debated; some were almost certainly used for grinding or processing grain or medicinal plants, while others accumulated associations with healing, cursing, or the veneration of local saints. The water that collects in them was sometimes held to have curative properties. This particular example at Garranes sits in an evocative position, on the south-eastern bank of the Cloghane River, with the sound of falling water close by. Whether that proximity to the waterfall was incidental or deliberate when the hollow was first made is not something the stone itself will tell you.