At Knockboy in County Waterford, there is an archaeological monument that you can stand directly on top of and not know it is there. A circular earthwork enclosure, roughly 25 metres across, sits on level pasture and registers no visible feature whatsoever at ground level. It is, in the most literal sense, an invisible site.

The enclosure was first recorded cartographically on the 1840 edition of the Ordnance Survey six-inch map, where it appears as a faint circular mark in the landscape. Earthwork enclosures of this kind are among the most common monument types in the Irish archaeological record; they range from the familiar raised ringfort, with its banks and ditches still legible in a field, to sites like this one, where centuries of ploughing, grazing, and soil movement have reduced all surface expression to nothing. What remains, if anything does, lies beneath the grass. The monument was formally classified as an earthwork site in 1995, a designation that acknowledges its likely archaeological significance while also conceding that the evidence for it is now essentially cartographic rather than physical.