Somewhere beneath the farmland at Plunketstown in County Kildare, a large enclosure lies entirely out of sight, revealed not by excavation or fieldwork but by the grass growing above it. On a dry summer's day, when crops are stressed and soil moisture varies with what lies beneath the surface, the buried ditches of a double-ringed enclosure cast their outline upward in the form of a cropmark, a faint but legible signature readable only from the air.

The enclosure is bivallate, meaning it was originally defined by two concentric circuits of banks and ditches rather than one, a form associated in Ireland with higher-status settlements of the early medieval period, though without excavation it is impossible to pin down a precise date or function for this particular example. Its internal dimensions are roughly 60 metres north to south and 88 metres east to west, making it a substantial feature, and its irregular shape sets it apart from the more geometrically regular ringforts that dot the Irish countryside. The cropmark was identified on Google Earth aerial imagery captured in July 2018, a time of year when dry conditions tend to bring such features into sharpest relief, and the discovery was documented shortly afterwards.