The depression is grass-covered and easy to miss, but its dimensions are specific enough to be suggestive: roughly three metres north to south and eight metres east to west, sinking about three-quarters of a metre below the surrounding ground at its deepest point before gradually levelling off towards the east.

The souterrain sits within a rath, the Irish term for a ringfort, a type of enclosed farmstead that was the dominant settlement form in Ireland from roughly the fifth to the twelfth century. Raths were defined by one or more earthen banks and ditches, and many contained souterrains dug beneath the interior. At Carrowkeribly, the depression begins close to the inner face of the enclosing bank and extends inward for eight metres. The fact that it partly intrudes into that bank is itself a detail worth noting, suggesting the souterrain was designed to make use of the bank's mass, perhaps for structural support or insulation. No stone lining is visible on the exposed sides; the construction here appears to be earthen rather than the dry-stone walling seen in souterrains elsewhere in the country. Whether a stone-built passage survives intact below the surface, or whether the original structure was always earthen, remains an open question, since the site has not been excavated.