It is a souterrain, a type of drystone-built underground passage constructed in early medieval Ireland, typically associated with ringforts and cashels, and used variously for storage, refuge, or as a means of concealed movement. This particular example is in poor condition, but enough survives to make out its essential form.

The souterrain runs to more than twelve metres in total length and follows a rough L-shape underground. It comprises two passages joined by a creep, which is a deliberately low and narrow connecting section, sometimes interpreted as a defensive feature that would force an intruder to move slowly and vulnerably between chambers. The first passage, measuring around 5.3 metres long, runs north-east to south-west and is entered from the south-western end. Just inside that access point, in the eastern wall, there is a blocked creep, only 0.4 metres high, its original purpose now sealed off. The second passage extends roughly north-west to south-east from the first, and entry to it today requires passing through a gap left by a collapsed roof lintel. Both passages are of similar width, around 1.6 metres, and possible air vents have been identified in the north-west corner of the first passage and in the west wall of the second. These small vents, if that is what they are, would have allowed some circulation of air into an otherwise sealed underground space, hinting at a structure intended for more than brief or occasional use. The cashel it sits within, a type of stone-walled enclosure associated with early medieval settlement in Ireland, provides the wider context for what was likely a working agricultural and domestic complex.