Others exist only as a trick of the light, visible solely from the air under the right conditions. The enclosure at Lissanisky, in north County Cork, belongs to that second, quieter category. It survives not as a physical presence on the ground but as a cropmark, a phenomenon where buried ditches and features cause the vegetation above them to grow differently, producing patterns legible only in aerial photographs. In this case, the image captured in July 1989 revealed the ghostly outlines of two concentric fosses, that is, ditches, forming a roughly circular enclosure approximately 40 metres in diameter.

The double-foss arrangement is significant. A single enclosing ditch is common enough in the Irish landscape, associated with ringforts and other early medieval settlements. Two concentric ones suggest either added defensive intention or a more complex history of use, possibly a site of some local importance whose ditches were dug or modified at different times. The enclosure's circular form and scale are broadly consistent with a ringfort, though without excavation the date and function remain open questions. What the 1989 aerial photograph also showed is that the site has not survived intact. The enclosure is truncated to the south-west by a field fence, meaning later agricultural boundaries have cut through and erased part of the original circuit, leaving only the cropmark as evidence that something more complete once existed here.