A souterrain, to give the structure its proper name, is a man-made underground passage or chamber cut into the earth or built from stone, most commonly associated with early medieval Irish settlements. They are found across Ireland and were likely used for storage, refuge, or both. This particular example remained sealed long enough that its discovery felt, in archaeological terms, almost accidental.

The structure consists of two roughly rectangular earth-cut chambers connected by a narrow creepway, a low linking passage just 0.6 metres wide and equally low in height, through which a person would have had to crawl. The first chamber runs along a northwest to southeast axis, measures around 4.6 metres in length and reaches a maximum width of 2 metres, with a height of just 1.2 metres. Access today is through the southeast end, where the barrel-vaulted roof, a curved arch of earth or stone overhead, has partially collapsed. That creepway at the southeast end of the first chamber leads to the northern end of the second, which runs roughly north to south and is of similar dimensions, though it has suffered considerably more collapse. Both chambers share a construction shaft, the original excavation point used when the souterrain was built, which offers a rare glimpse into how such structures were engineered from above before being sealed over.