Rather than being dug into the earth, this ancient passage was cleverly built against a natural rock bank, with its remaining walls constructed from carefully placed boulders. The builders incorporated two small window openings that overlooked a nearby stream, which ran alongside the passage; a rather unusual feature that would have provided both light and a connection to the outside world.

The passage itself measured at least six feet in length, though its collapsed end suggests it originally extended further. The entrance was remarkably small, standing just one foot seven inches high and two feet wide, requiring anyone entering to crouch or crawl through. Above, the structure was roofed with two substantial flagstones, carefully sealed with smaller stones packed between them to keep out the elements. This construction technique shows considerable skill in creating a weatherproof shelter using only the materials at hand.

Archaeological surveys suggest this site bears a striking resemblance to St. Faned's Cell, another souterrain located elsewhere in the county. These structures, typically dating from the early medieval period, served various purposes; from storage spaces and refuges to places of religious retreat. The Lackcrom souterrain's unique above-ground construction and stream-facing windows hint at a builder who adapted traditional designs to work with the natural landscape, creating a distinctive variation on an ancient architectural form.