The site sits within a rath, a type of enclosed farmstead built and occupied during the early medieval period, typically defined by one or more earthen banks and ditches. Inside that enclosure, local tradition holds that a souterrain was once accessible. A souterrain is an underground stone-built passage or chamber, constructed using drystone walling and covered with flat lintel stones laid across the top. They were common features of early medieval settlements across Ireland, used variously for storage, refuge, or ventilation. At Brackloon, the entrance was blocked up at some point in the past, and the interior has not been accessible since.

What remains visible above ground is suggestive rather than conclusive. Two large stone slabs protrude obliquely from the grass to the west of the rath's centre, angled in a way that distinguishes them from ordinary field clearance. These may mark the location of the blocked passage below, the lintel stones of a collapsed or deliberately sealed entrance pressing upward through the turf. No excavation appears to have been carried out, and the tradition of the souterrain rests on local memory rather than documented investigation. That combination, an earthwork of early medieval origin, a blocked underground structure, and two anomalous stones breaking the surface at an odd angle, gives the site a quality common to many Irish monuments: most of what it contains remains out of reach.