It runs east to west, measures more than ten and a half metres in length, and is built entirely from drystone, meaning its walls and likely its roof were constructed without mortar, each stone relying on the weight and fit of its neighbours to hold the whole thing together. It is currently inaccessible, which gives it an odd quality among archaeological features: it is neither lost nor found, simply sealed.

The chamber sits within a cashel, a type of stone-walled ringfort characteristic of early medieval Ireland, in which a roughly circular enclosure defined by a substantial drystone wall would have protected a farmstead or the household of a person of local standing. The Roo example carries its own monument reference, and the cave or souterrain within it, a souterrain being an underground or semi-underground passage typically used for storage or refuge, was noted by McCaffrey as far back as 1952. That reference places scholarly awareness of the feature at least seventy years ago, though the structure itself almost certainly predates any modern record by many centuries. The east-west orientation is a detail worth holding onto; such alignments in early Irish monuments are not always incidental, though whether it reflects practical, symbolic, or simply topographical reasoning here is not something the surviving evidence can answer.