A low, grass-covered ridge, seven or eight metres long and no more than half a metre high, rises from the limestone pasture. A shallow, grassed-over hollow at its northern end, its edges still partly lined with drystone walling, is the most obvious clue that something lies below. What the ground conceals is a souterrain, an early medieval underground structure, typically built for storage or refuge, consisting here of three well-built interconnected chambers arranged in a roughly north-south line and constructed using a combination of drystone masonry and rock-cut technique.

The entrance, such as it survives, narrows immediately into a low creep, a deliberately constricted passage that forces anyone entering to crawl, and which opens into Chamber 1 at the level of the roof rather than the floor, a drop of roughly a metre. The floor of this first chamber slopes or steps downward toward its southern end, though accumulated soil and rubble now obscure the original surface. A second creep in the southern wall leads into Chamber 2, the largest of the three, where the builders cut the lower walls directly from bedrock before continuing upward in drystone, finishing the uppermost course with corbelled limestone blocks to carry the roof lintels. Set into the western wall of this chamber, at about knee height, is a small rectangular recess, barely thirty centimetres in any direction, roofed with a single flat stone; a wall cupboard of a kind found occasionally in Irish souterrains, presumably for keeping small objects dry and to hand. Chamber 3, at the southern end of the sequence, is built along the same lines, its back wall formed almost entirely of natural bedrock rising to just below roof level. It too has a neat rectangular recess in its western wall, and in its south-east corner a narrow natural fissure in the bedrock opens at floor level, too tight to enter.

The souterrain sits within a remarkably dense cluster of early medieval remains. A rath, a circular earthen enclosure of the kind used as a defended farmstead, lies just twenty-five metres to the north-west, and a cashel, its stone-walled equivalent, stands roughly the same distance to the west. Souterrains of this kind are almost always found in association with such settlements, serving the households built above and around them, and the Lecarrow example, with its carefully built chambers, its small domestic recesses, and its bedrock-cut lower walls, gives a precise and unusually well-preserved picture of that underground world.