The opening measures just eighteen inches wide and twelve inches high, which is less a doorway than a deliberate squeeze, and it leads into a passage running roughly ten feet eastward directly into the cliff face. This is a souterrain, an underground stone-lined passage or chamber of the kind built throughout early medieval Ireland, typically used for storage, refuge, or both.

The passage was recorded by Hartnett in 1939, who noted its modest but carefully constructed form. The side walls are built in dry masonry, meaning the stones are fitted together without mortar, and they incline inward as they rise, narrowing toward the roof. Flat slabs laid across the top complete the structure. This corbelled or inclining-wall technique is characteristic of early Irish souterrains, and it allowed builders to create a stable covered space without the need for cut stone or dressed masonry. The souterrain sits within a cliff-edge fort, a type of coastal or elevated promontory enclosure where natural drops on one or more sides provide part of the defensive boundary, reducing the amount of artificial walling required.