Fewer realise they are walking across something considerably older. Just to the south-east of the lodge sit two passage tombs, one of which survives as a hollowed-out mound measuring roughly 26 metres east to west and 18.8 metres north to south, rising to about 1.5 metres. A passage tomb is a type of megalithic burial monument in which a stone-lined corridor leads to a central chamber, the whole structure typically covered by a cairn of loose stone or earth. The mound here is enclosed by a shallow ditch, and the monument may have been reworked into a ring-barrow, a circular earthwork of a rather different function, at some point in prehistory. The two tombs form part of a wider cluster distributed along the northern and western slopes of the Dublin and Wicklow mountains.

The lodge beside it is, in a grim irony, partly responsible for the tomb's deterioration. When the antiquarian Austin Cooper visited in 1779, he recorded kerbstones still visible along the southern perimeter, large flat stones set on edge to form a low boundary wall enclosing a heap of smaller stones. He noted a central stone nine feet long and six feet broad lying flat, and puzzled pleasantly over a standing stone roughly sixty yards to the south-west, unsure whether it was part of the prehistoric complex or simply a scratching post for cattle. By Cooper's time, part of the cairn had already been quarried away to provide building material for the lodge itself, constructed for a Mr Connolly. A 2016 research excavation funded by Dublin South County Council confirmed that the ditch enclosing the monument was most likely a robber trench, cut when kerbstones were removed for use in the construction of the Old Military Road at the beginning of the nineteenth century. The excavation, directed under licence 16E0497, did recover original cairn material, along with a polished stone axehead and a decorated stone that may, pending further analysis, belong to the corpus of megalithic art.

The hill is accessible via a well-used trail from the Montpelier car park on the R115. The approach is steep in places and can be muddy after rain. The forestry to the south and west limits views in those directions, but the northern and eastern panoramas across Dublin are open and wide. The tomb sits immediately beside the Hell Fire Club ruin, and it is easy to walk past it without recognising what the low, irregular mound represents. The companion tomb lies adjacent. Neither is fenced or signposted in any elaborate way, which means paying attention to the ground rather than just the ruin beside it.