Somewhere in the Clontarf area of north Dublin, two mounds were once considered significant enough to be listed in an official planning document, yet no one can say with confidence where they actually are. They exist, at least on paper, as a category of place rather than a location.

The City Development Plan of 1991 includes a reference to a 'site of mounds', noting two such features in Clontarf. Beyond that, the record offers little. Mounds of this kind, where they survive elsewhere in Ireland, can represent anything from prehistoric burial cairns to medieval earthworks or even much later landscape features, though without further survey or excavation it is rarely possible to say which. Clontarf itself carries considerable historical weight, most famously as the site of the 1014 battle in which the High King Brian Boru defeated a Norse and Leinster alliance, and the broader area has been settled and reshaped over many centuries. Whether these mounds had any connection to that longer history, or were simply earthen features that caught a surveyor's eye at some point before the record was made, remains entirely open.

In practical terms, there is no specific location to visit. The monument falls into an unusual category in Irish archaeological recording, present in the archive but absent from the landscape as far as current knowledge allows. It is possible that the mounds were lost to development, subsumed into gardens or roads or built structures during the twentieth century, which was a period of considerable suburban expansion across coastal Dublin. Anyone with a strong interest in the area might find it worth consulting the Dublin City Council planning archives or the Sites and Monuments Record for any subsequent survey notes, though the honest answer, for now, is that these two mounds are known only as an absence.