This is a souterrain, an artificial underground structure of the kind built throughout early medieval Ireland, typically used for storage or refuge, and sometimes as a place to shelter food or people in times of threat. What makes this one quietly unusual is that its walls are not dressed or laid stone but natural weathered grykes, the solution-carved fissures characteristic of the Burren's limestone bedrock. Someone, at some point, found a crack in the rock and extended or enclosed it, letting the landscape do much of the structural work.

The souterrain sits within the north-western centre of a stone-walled enclosure and runs roughly north to south, with its entrance at the northern end. The lintel stone capping that entrance is about fifteen centimetres thick, which gives a sense of how tightly the whole thing is fitted together. A field visit in 2007 found the passage entirely inaccessible. It was not until 2019 that a researcher named Bowmer was able to enter and record it, finding a passage at least two metres in length. The floor at that point was covered in boulders, animal bones, and modern waste, the accumulated debris of a structure that had been sealed, forgotten, and intermittently rediscovered over an unknown stretch of time.