What exists here exists only from the air, briefly, under the right conditions: two concentric circular ditches, known as fosses, pressed into the soil of a North Cork field and legible only when a dry summer draws them up through a ripening crop as faint discolourations in the growth above. It is a ghost of an enclosure, roughly thirty metres across, known to archaeology almost entirely through a single aerial photograph taken in July 1989.

Cropmark archaeology works because buried features, whether filled-in ditches or the compressed soil of old walls, affect how plants grow above them. Ditches retain moisture; their overlying crops stay greener longer and grow taller. Compacted surfaces do the opposite. From the ground these differences are invisible, but from above they resolve into shapes, and sometimes those shapes are recognisable. At Ballylegan, what resolved into view was a double-fossed circular enclosure with what appears to be an entrance gap through the outer ditch to the north. Such enclosures are broadly associated with early medieval settlement in Ireland, though without excavation their precise date and function remain open questions. The site does not stand alone in the landscape; a second circular enclosure and a ringfort lie roughly a hundred and fifty metres to the south-east, suggesting this part of North Cork was once considerably more occupied than its present fields might suggest.