No earthwork survives above the surface, no ring of stones marks the spot; what exists is a pattern of post pits, the buried ghosts of timber uprights that once formed a small oval structure, roughly fifteen metres north to south and ten metres east to west. It is precisely the kind of site that centuries of ploughing and weathering can erase entirely, leaving nothing for a casual walker to notice.

The enclosure came to light through a geophysical survey carried out under Licence 13R084 by the Discovery Programme, the Irish state-funded body dedicated to archaeological research. The work was conducted as part of the 'Late Iron Age and "Roman" Ireland' project, an initiative examining the period roughly spanning the last few centuries before and after the turn of the first millennium, when Ireland had no Roman occupation of its own but was nonetheless in contact, through trade and other exchange, with the Roman world. The survey located this oval setting of post pits approximately forty metres northeast of the summit of the main hilltop enclosure already recorded at the site. Post pits are the holes, sometimes stone-packed, that held the upright timbers of a structure; when the posts decay or are removed, the disturbed soil they leave behind can still be detected through techniques such as magnetometry or earth resistance survey, even when nothing is visible on the surface. The findings were published by Dowling in 2015.

Knockbrack sits in north Dublin, and the recorded site is catalogued under the reference DU004-012006. Because the enclosure is a subsurface feature rather than a visible monument, a visit to the hill offers landscape context rather than a clear structure to examine. The hilltop itself, and its relationship to the surrounding terrain, gives some sense of why this elevated position was chosen in the first place. Anyone with a serious interest in the site would do well to consult the Discovery Programme's published findings before visiting, since without that background the ground underfoot reveals very little of what is known to lie beneath it.