Detected not by spade but by geophysical survey, it exists on paper and in data rather than in any physical exposure, which is part of what makes it so intriguing.

The structure was identified through a geophysical survey, carried out under Licence no. 12R127 by the Discovery Programme as part of their 'Late Iron Age and "Roman" Ireland' project. That project takes its name from a genuinely unusual problem: Drumanagh is a promontory fort, a type of enclosure that uses coastal cliffs and constructed earthworks to enclose a headland, and it has long been associated with finds suggesting contact, possibly significant contact, with Roman Britain. The geophysical work recorded a circular structure measuring approximately twelve metres in diameter in the southern half of the enclosure, catalogued as part of the wider site reference DU008-006004-. A number of possible pit-type features were also noted in its vicinity. The findings were reported by Dowling in 2014. Whether the structure is a roundhouse, a ritual enclosure, or something else entirely remains an open question; without excavation, the data can suggest but not confirm.

Drumanagh itself sits on a headland at Loughshinny, north of Skerries, and is not easily accessible to casual visitors. The earthworks are on private farmland, and the site has a complicated history regarding access and the circumstances of earlier, reportedly illicit metal-detecting activity on the headland. Those approaching from the coastal path can appreciate the scale of the promontory and the logic of its location without setting foot on the enclosed area. The survey findings, including this structure, are part of an ongoing effort to understand the site without disturbing it, which means the most significant features remain invisible at ground level. That invisibility is, in a sense, the point.