Within the interior of this rath, a souterrain has been recorded, giving the site a subterranean dimension that the modest surface remains do little to advertise.

A rath is a ringfort of earthen construction, the most common type of early medieval settlement monument in Ireland, typically dating from roughly the sixth to the tenth century. They were farmsteads rather than forts in any military sense, the enclosing bank serving to define a household's space and keep livestock in or out. The souterrain associated with this one is an underground stone-built passage or chamber, a feature found in many ringforts and thought to have served variously for storage, refuge, or ventilation of perishables. At Maulnagirra, only the arc of bank running from the eastern to the southern side remains legible as an earthwork, the rest of the circuit presumably lost to centuries of agricultural use on the surrounding slope.