They left no trace above ground. No wheel, no millstone, no crumbling wall survives to mark their presence. What remains is largely a matter of record, a name on old documents and a location pinned to a map.

Known as the Kings Mills, the watermills were constructed in the early thirteenth century, placing their origins in the decades when Dublin Castle itself was being established as the seat of English royal authority in Ireland. A watermill, at its simplest, is a structure that harnesses flowing water to power a millstone for grinding grain, and the presence of such mills within the castle complex would have served the considerable practical needs of the garrison and administration housed there. The mills were still standing as late as the seventeenth century, a span of roughly four hundred years of operation, before they eventually disappeared from the landscape entirely. Their location within the lower yard of the castle has been established through historical cartography, specifically the FMD map of 1978, while the documentary record draws on John T. Gilbert's nineteenth-century compilation of Dublin records and later survey work by Bradley and King.

For anyone visiting Dublin Castle today, the lower yard is accessible as part of the general castle complex in the city centre, and the area is well-worn ground for anyone who has queued for a guided tour or cut through on their way to the Chester Beatty Library. There is nothing to see at the mill site specifically; no interpretive panel marks the spot, and the ground gives nothing away. The value, if any, is in knowing what is underfoot, and in the slight adjustment of perspective that comes with it. Medieval industrial infrastructure, quietly buried beneath one of the most visited sites in the Irish capital, unannounced and unremarked.