It occupies a quiet position roughly 300 metres from sea cliffs that drop some ten metres to the shore below. None of that immediately suggests an ancient monument of uncertain purpose, which is part of what makes this place so quietly odd.

The earthwork consists of two concentric banks, a form that archaeologists sometimes call a bivallate rath, though a rath typically served as an enclosed farmstead for an early medieval family. This one resists that tidy classification. Its interior diameter runs to 62 metres, and the outer bank is notably massive, measuring up to 15.5 metres wide with an external height of around 5.5 metres. Writing in 1921, Dalton argued it might instead be a sub-Roman or Celtic cult centre, perhaps a site of ceremony rather than daily life. The scale and unusual regularity of the banks lend some weight to that idea, though no burial monuments or other ceremonial features have been identified nearby, which makes the case difficult to settle either way. A souterrain, an underground passage of the kind sometimes found beneath early Irish settlement sites, was reportedly discovered at the centre in 1908, though this has not been excavated. The site's strange layering continued into the nineteenth century. Around 1680, a writer named Sutton attributed the banks to the Danes, a catch-all explanation that was commonly applied to mysterious earthworks of the period. By 1839, the Ordnance Survey was marking it on its six-inch map under the name Mulgrave Rath Observatory, a title recorded by the scholar John O'Donovan around 1840. O'Donovan noted that the local proprietor had named it after Lord Mulgrave, who served as Lord Lieutenant of Ireland between 1835 and 1839, and had installed an actual observatory within the enclosure and built the surrounding wall. The result is a prehistoric or early medieval monument that spent part of the Victorian era as a stargazing platform, and now sits at the centre of a garden, its origins still genuinely unresolved.