This one exists, at least for most purposes, only from the air. At Ballyhimock in north County Cork, a circular enclosure roughly 25 metres across is known almost entirely through a cropmark, the kind of faint discolouration in a growing field that becomes legible only when viewed from altitude. Cropmarks form when buried ditches or other disturbances alter how soil retains moisture, causing the vegetation above to grow differently, often a shade greener or more lush over a filled ditch, and that differential growth becomes visible in aerial photographs under the right conditions of season and light.

The enclosure was identified in a photograph taken in July 1989 as part of an aerial survey programme covering Cork. What the image shows is the cropmark of a fosse, that is, a ditch, tracing a circle in the ground below. The structure it once defined was likely an enclosed settlement of some kind, though without excavation the precise date and function remain open questions. It sits within a landscape that carries other traces of past occupation: a ringfort lies roughly 260 metres to the south-east, and a field system extends to the north and east. A ringfort, to use the term broadly, is a circular enclosure defined by an earthen bank and ditch, common across Ireland from roughly the early medieval period, and used variously as farmsteads, livestock enclosures, or defended homesteads. Whether the Ballyhimock enclosure belongs to the same broad tradition, or represents something earlier or later, is not established. What is clear is that this particular patch of Cork farmland holds, invisibly underfoot, the ghost of a structure that was once significant enough to leave a mark in the soil that persists more than a thousand years later.