The one at Carrigdangan in County Cork went entirely unnoticed until 1988, when workers clearing a field fence broke through into something that had been sealed beneath the ground for centuries. Its original entrance has never been located, which means it was not simply forgotten; it was lost.

What survives consists of at least three earth-cut chambers connected by creepways, the low, narrow connecting passages that force anyone moving between chambers to crouch or crawl. The first chamber measures roughly 2.75 metres long and just 1.3 metres wide, and it is now entered from above through a hole in the roof rather than by any original route. A creepway on its western side leads east into a second, slightly broader chamber, 2.38 metres long and over two metres wide. That second chamber has a construction shaft at its south-eastern side, a feature that would have been dug during the original building process and then sealed. A further creepway at the south-western side of this chamber once connected to a third, but that third chamber has since collapsed, and investigation stops there. How many more passages or chambers might lie beyond the collapse is unknown.

The measurements give a sense of how confined the space is: head height throughout is barely above a metre, meaning the souterrain was never designed for comfortable occupation but rather for crouching figures moving quickly, or for goods stacked low in the dark. The fact that no original entrance has been found leaves open the question of how it was accessed in use, and from which direction whoever built it expected people to come and go.