These stone-lined passages, built during the early medieval period, were constructed beneath the ground as places of refuge or storage, their roofs sealed by heavy capstones and concealed beneath the earth. The one at Sheshymore in County Clare does something different. It sits above ground, its three large lintels visible at the surface, its walls rising to just over a metre in height before narrowing inward in a slight corbelling technique, where each course of stone projects fractionally inward beyond the one below, drawing the walls closer together toward the top. It is a small structure by any measure, roughly three and a half metres from north to south and just over a metre and a half wide, but the detail in its construction is considered.

The souterrain sits to the north-north-west of the centre of a cashel, a type of early medieval stone-walled enclosure typically associated with farmsteads or the settlements of minor lords. That cashel is now poorly preserved, which makes the relative survival of its associated souterrain all the more notable. The walls of the souterrain extend further northward beyond the roofed section, unroofed and open to the sky, with an accumulation of clay immediately to their north. A mound about one and a half metres high curves around the southern end of the structure, giving the whole feature a slightly buried, half-emergent quality, as if the landscape has been slowly reclaiming it from one direction while leaving the rest exposed. The relationship between these unroofed wall extensions and the clay deposit to the north is not fully explained, but the arrangement suggests the original structure may have been more extensive than what survives today.