A killeen, in Irish tradition, was an unconsecrated burial ground reserved for unbaptised infants, and the upright slabs and loose stones scattered across the southern half of the interior are thought to be directly connected to that use. But the enclosure itself is considerably older and more substantial: a caher, the Irish term for a stone-walled ringfort, roughly oval in plan and measuring 22 metres north to south and 18 metres east to west. A tributary of the Finglas river runs along its eastern side, and from its position the site looks out over Ballinskelligs Bay to the north-west.

The enclosing wall, though poorly preserved and standing only about half a metre high, is still 2.3 metres wide, built from flat slabs facing both inner and outer surfaces with a rubble core packed between them. Its most striking feature is the entrance at the north-east: a passage nearly a metre wide and just over two metres long, lined with orthostats, the large upright standing stones that give it a corridor-like formality. Six orthostats survive across both sides of the passage, some still standing over a metre tall, though the passageway itself is now choked with smaller stones and a fallen upright. The interior, particularly its northern half, contains the remains of circular and rectangular structures that appear to be relatively recent additions, though a reference from 1957 by a researcher named Henry documented three round stone huts in that same area, suggesting earlier buildings may lie beneath. Outside the main wall, two small hut foundations cling to the north-north-east exterior, their walls largely collapsed and overgrown. The Ordnance Survey Name Books recorded that penances were performed at the site on Good Fridays, a detail that places this ruinous caher within a living pattern of popular religious practice long after its original function had been forgotten.