The southern of the pair, sitting at a spot known as Knockaniller in the townland of Slievethoul, is a substantial presence on the landscape: a kerbed cairn, roughly circular and round-topped, approximately forty metres across and five metres high. A kerbed cairn is a mound of stone and earth held at its base by a ring of larger stones, a construction technique common to the passage tomb tradition of Neolithic Ireland. Passage tombs are among the oldest monument types in the country, typically consisting of a stone-lined corridor leading to a burial chamber, all covered by such a mound. This one sits immediately south of its neighbour, the two forming a pair that has received relatively little public attention compared to better-known groupings elsewhere in the country.

The site is documented in the work of Michael Herity, whose studies of Irish passage tombs, published in 1974 and again in 2001, provide the primary record of both monuments at this location. Herity catalogued the Knockaniller cairn alongside its northern companion, noting the proximity of the two and the unusual circumstance of the townland boundary running between them. That boundary is a medieval or early modern feature at the earliest, imposed on a landscape already thousands of years old by the time anyone thought to draw administrative lines across it. The hill itself, Saggart Hill in south County Dublin, sits within a broader region that contains scattered traces of prehistoric activity, though this particular pair of tombs remains relatively obscure.

The site is not formally developed for visitors, and the condition of the cairn reflects that. Machine tracks run across the top of the mound, and much of the surface is covered in fern, giving it a rougher, more overgrown appearance than the impression one might have of a monument of this scale. Reaching Knockaniller requires some cross-country walking on the northern slope of Saggart Hill; the terrain is uneven and the monument sits without signage or formal access. Those familiar with reading an Ordnance Survey map will have the most straightforward time locating it. The companion tomb to the north lies close enough that both can be taken in on the same visit, and seeing the two together, with that townland line running silently between them, gives a clearer sense of how modern geography has been laid over a much older arrangement.