It measures roughly seven feet by four, just large enough for a small group of people to huddle in, and the only way in or out is through a hole barely two feet wide and one foot tall. Nobody has entered it in living memory, and from the surface today there is nothing to see at all.

A souterrain is an underground chamber, typically stone-lined, built during the early medieval period and associated with ringforts across Ireland. Their precise purpose is still debated, though storage and refuge are the most commonly cited explanations. The Knockagarrane example sits within such a ringfort and was recorded in 1934 by a researcher named Bowman, who noted not only the cramped entrance and modest dimensions of the chamber, but also the fact that its lining stones had already been removed by that point. Stone was a useful commodity, and the robbing out of archaeological structures for building material was commonplace across rural Ireland for centuries. What Bowman found, in other words, was already a diminished thing: the bones of a structure rather than the structure itself. Whether the chamber remains intact beneath the soil, or has partially collapsed in the decades since that visit, is not recorded.