This is a stepped barrow, a form of funerary earthwork in which a central mound is shaped into successive raised platforms, each one narrowing as it climbs. What makes this particular example arresting is not just its form but its scale and its crown: at the very top of the uppermost tier, a standing stone occupies the centre, lending the whole construction an almost deliberate, ceremonial verticality.

The monument measures roughly 53 metres across its longest axis, with a central mound rising between 3.4 and 4 metres above the surrounding ground. That mound is organised into three tiers. The broad, flat-topped basal platform extends approximately 35 metres across; above it a second tier, defined by a low scarp, rises within the eastern two-thirds of that platform; and above that again a third, smaller tier, about 10.5 metres across east to west, carries the standing stone at its centre. Encircling the mound are a fosse, a ditch-like depression between 2.2 and 3.5 metres wide, and beyond that an outer bank, now heavily overgrown and partially levelled by cattle. The name of the hill itself offers a clue to the monument's long prominence in the local imagination. George Cunningham, writing in 1980, suggested that Knockastoolery derives from the Irish Cnoc an Stualaire, meaning the hill of the gallan or high stone, a phrase that may well refer to the standing stone still visible at the summit. The name was already fixed in the cartographic record by 1842, when it appeared on the Ordnance Survey six-inch map, and it was still there on the 1920 edition.

The hill sits at the eastern end of a spur in an area of pastureland, and the views from the upper tiers are wide. The overgrowth is densest on the northern and eastern sides, where the fosse and outer bank are harder to trace, while the bank is best preserved from the south-west around to the north-west. The standing stone at the summit is visible from the north-east, rising above the scarp of the topmost tier.