The opening measures 1.3 metres by 1.1 metres and sits in the western quadrant of an enclosed site, with a second opening at the external base of the same enclosing wall. Beyond those two mouths, the passage is inaccessible, which is to say the interior has collapsed, silted, or simply closed itself off to inspection.

This is a souterrain, a type of underground stone-lined passage built during the early medieval period in Ireland, typically between the seventh and twelfth centuries. The word comes from the French for "underground passage", and while the precise function of souterrains is still debated, they are generally understood to have served as storage spaces, places of refuge, or both, exploiting the stable cool temperature of the subsoil. The Gortmaloon example is of drystone construction, meaning the passage walls were built without mortar, each stone selected and placed to hold its neighbours in position. The passage appears to run on a roughly northeast to southwest axis. The presence of two openings, one inside the enclosure and one at its outer wall, is a fairly typical arrangement, suggesting the souterrain was integrated into a larger enclosed settlement, possibly a ringfort. This is not an isolated curiosity but part of a landscape on the Iveragh Peninsula in south Kerry that is exceptionally dense with early medieval remains, as documented in the archaeological survey carried out by A. O'Sullivan and J. Sheehan and published by Cork University Press in 1996.