It has no wall, no ditch you could trip over, no visible monument to draw the eye. Its presence is revealed only during dry summers, when a broad band of parched vegetation, somewhere between three and four metres wide, traces a curve across the field, betraying the outline of an enclosure that has otherwise completely vanished into the earth.

A cropmark of this kind forms when buried features, perhaps the remains of a filled-in ditch or compacted soil, affect how plants above them absorb moisture. In a dry spell, grass or crops over denser or shallower ground lose water faster, turning yellow or brown in a pattern that mirrors whatever lies beneath. The Coolnaveagh enclosure was first spotted by Simon Dowling using Google Earth imagery captured in the summers of 2018, when the distinctive parch mark became legible from above. The circle can be followed around its southern, western, and northern arc, but the north-east to south portion of the perimeter is obscured by vehicle tracks crossing the field, which muddle the signal enough to break the trace. Without those tyre marks, a near-complete ring might be visible. The site sits on a fairly level stretch of landscape, the kind of unassuming ground where enclosures of this sort are easily overlooked for generations until a heatwave and a satellite pass at just the right moment.