A circular enclosure roughly ten metres across sits on a gentle east-facing slope just north of a low hilltop, and the only reason anyone knows it exists at all is because a camera mounted in an aircraft happened to look down at the right moment, in the right season, when the crop above it was growing unevenly over buried soil.

What the aerial photograph revealed is a cropmark, a faint but telling variation in vegetation caused by buried features altering how moisture and nutrients move through the earth. In this case, the defining feature appears to be a fosse, a cut ditch encircling the interior, which shows up from above even when it leaves no trace on the surface. The site is tentatively identified as a barrow, a type of burial monument found across prehistoric Ireland and Britain, typically constructed as a low earthen mound surrounded by a ditch. Whether any mound ever rose above the fosse at Knocknamuck, and whether it has since been ploughed or eroded flat, is not recorded. What remains is the ghost of a boundary, readable only from the sky.