A circular enclosure lies here, betrayed only from the air, where variations in crop growth trace the buried edges of a long-vanished structure. These cropmarks form when buried features such as ditches or walls affect how plants above them grow, producing faint but legible differences in colour and height that become visible under the right light and at the right season.

The enclosure came to light through aerial photography carried out in July 2006, when the distinctive circular cropmark was captured in images taken by M. Moore. It lies roughly 300 metres to the north-east of another recorded site in the same area, suggesting this part of Wicklow has a longer history of human activity than the surface landscape might suggest. Circular enclosures of this kind are found across Ireland and can date from the prehistoric period through to the early medieval, sometimes representing the remains of a ringfort, a type of enclosed farmstead that was the dominant form of rural settlement in early Christian Ireland, or possibly something older still. Without excavation, the date and function of the Ballynerrin enclosure remain open questions.