This one in Moher, County Tipperary, is visible only from the air, a ghostly outline pressed into the earth on a poorly drained, south-west-facing slope of upland ground, legible to a camera thousands of feet above but entirely invisible to anyone walking across it.

The enclosure was identified as a cropmark, a phenomenon that occurs when buried features, walls, ditches, or filled pits, affect how crops grow above them. Soil disturbed by an ancient ditch tends to retain more moisture, producing lusher, taller growth; a buried wall does the opposite. From the air, these subtle differences in vegetation read as shapes, outlines of structures that have otherwise vanished from the landscape. In this case, aerial photographs taken in April 1974 captured the enclosure on a GSI survey flight, preserving in photographic form what the upland terrain itself has long since swallowed. The waterlogged, slow-draining character of the slope has likely both obscured and, in its way, protected whatever lies beneath.