That, in its own way, is the point. Below the grass, or at least once below it, lay a fulacht fia, a type of prehistoric cooking site found in large numbers across Ireland, typically identified by a horseshoe-shaped mound of heat-shattered stone and charcoal left over from the repeated boiling of water. This one left no surface trace. Its existence was recorded only because land reclamation work turned up burnt material, and local knowledge put a name to what had been disturbed.

What makes the site slightly stranger than its invisibility alone is the fate of a mass rock that was once positioned within the fulacht fia itself. Mass rocks are flat stones, usually set in remote or concealed spots, where Catholic priests celebrated Mass illegally during the Penal Law period, roughly the late seventeenth and early eighteenth centuries, when public worship was suppressed. The choice of an already-ancient earthwork as the setting for one of these clandestine altars was not unusual; such places were often marginal, out of sight, and already outside the ordinary pattern of land use. At Garranes, that mass rock has since been moved and now sits embedded in a field fence to the south of the original site, which means two distinct layers of history, one prehistoric, one early modern, have both been displaced from their original contexts and survive only partially, and only just.