That uncertainty is, in a sense, the whole story. A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval ringforts, and used variously for storage, refuge, or shelter. At Rathgorgin, even the ringfort it once belonged to has effectively ceased to exist above ground.

The trail of evidence is thin but traceable. Writing in 1916, Orpen noted a trace of a souterrain lying close to the inner rampart of a rath, the circular earthwork enclosure that would have been its companion structure. When Cody revisited the site in 1989, the rath had been levelled entirely, and nothing of either feature remained visible at the surface. The only sign that anything had ever been there was a slight roughness in the grass, the kind of irregularity that most walkers would pass without a second glance.