The surveyors recorded it plainly as "Cardiff castle in ruins", marking an L-shaped building to the north of the road, the kind of laconic notation that hints at something once substantial enough to name a place after, yet already lost to practical use. Today, the site has been swallowed by later development and nothing remains visible at ground level, making this one of those places that exists more fully on paper than in the landscape.

The name itself points to a 17th-century house of some standing, likely a fortified or semi-fortified structure of the sort common in the Dublin hinterland during that period. In the 1600s, such buildings often combined domestic function with defensive features, reflecting the uncertainties of plantation-era Ireland. The L-shaped plan recorded by the Ordnance Survey was a recognised form for vernacular gentry houses of the period, allowing for a degree of internal organisation while presenting a relatively defensible profile. That the map already describes it as ruinous by 1837 suggests a decline well underway before the Victorian era, though the precise circumstances of its abandonment are not documented in the surviving record.

There is, in a strict sense, nothing left to visit. The ground-level archaeology, if any survives beneath the later development, is inaccessible to the casual observer. What remains is the cartographic trace: the first edition OS six-inch map, available through the Irish Historic Maps viewer, still shows the outline of that L-shaped footprint north of the road, annotated in the surveyors' careful hand. For anyone interested in the vanished built fabric of early modern Dublin, these maps repay close attention, documenting structures that left no other mark. The work of recording this site was carried out by Geraldine Stout, whose notes were compiled in August 2011.