The hillfort on Knockadigeen Hill, sitting at the northern edge of the Silvermines Mountain range in County Tipperary, is the kind of monument that survives more as an idea than as an obvious physical presence, yet its earthworks trace an oval circuit roughly 190 metres north to south and 280 metres east to west around the hill's summit, which is no small statement of ambition from whoever built it.

Hillforts, broadly speaking, are large enclosed sites defined by banks and ditches that follow the natural contours of elevated ground. On Knockadigeen the defences consist of a fosse, an earthen bank, and an outer fosse, with traces of a further external bank surviving at the north-north-west. The system is univallate in the sense that a single main rampart defines the circuit, though the layering of ditches and banks gives it more complexity than that word implies. No entrance has been identified on the ground or from the air. Aerial photography did reveal what appears to be a small enclosure inside the fort to the east, but nothing of it is visible at ground level. The site does not appear on any historic mapping, which means it dropped entirely out of living memory and documentary record until modern survey work brought it back into focus. A nearby hillfort at Ballincurra lies about 1.4 kilometres to the south-west, suggesting this part of the Silvermines range supported more than one such monument.

The north-east quadrant is the best-preserved section of the circuit, largely because the commercial forestry planted across much of the hill around 1991 has not encroached there. Elsewhere, ploughing associated with that planting has damaged the ramparts considerably. The interior is covered in dense gorse and heather, and the ground-level experience of the site is shaped as much by that vegetation and the tree cover as by anything recognisably archaeological. The E-W townland boundary between Knockadigeen and Cloghonan cuts through the western portion of the fort, an administrative line drawn in a much later era that now runs straight across a monument old enough to have no recorded history at all.