This particular structure, stretching approximately four metres from north to south, showcases the impressive drystone construction techniques of its builders. The walls, standing about a metre high and 1.2 metres wide, were carefully assembled without mortar, relying solely on the skill of placing stones to create a stable underground chamber.

The souterrain reveals intriguing architectural details that hint at its original design and purpose. At its northern end, the passage narrows dramatically to just half a metre wide, where a stone slab bridges the gap at mid-height before the tunnel disappears into collapsed earth. The southern terminus tells a different story; here, the walls meet in a squared-off fashion, suggesting this was likely one of the structure's original entrances. Four stone lintels still crown portions of the passage, remnants of what would have been a complete roof system. Adding to the site's mystery, another slab visible in the ground about three metres east of the northern end hints that this underground network may have been more extensive than what remains visible today.

These souterrains, found throughout Ireland but particularly common in Ulster, served multiple purposes for early medieval communities between roughly 500 and 1200 AD. They may have functioned as storage facilities for valuable goods and food supplies, temporary refuges during raids, or even held ritual significance. The Cratlagh example, surrounded by rough terrain but near good pasture land, would have been ideally positioned to serve a farming community, offering both practical storage solutions and a measure of security in uncertain times.