Nobody has confirmed it recently. There is no visible surface trace, and the interior of the ringfort itself is now planted with trees, which makes any survey of the ground considerably harder.

A souterrain is an underground passage or chamber, typically dry-stone built, associated with early medieval ringforts throughout Ireland. They were used variously for storage, refuge, or ventilation, and are far more common across the Irish countryside than most people realise, the majority hidden beneath farmland or overgrown earthworks. The detail that makes Coolanarney slightly unusual is the reach of this one. In 1937, a researcher named Broker recorded it as an underground passage crossing the road to the south, which implies a structure extending well beyond the ringfort's own enclosure. Whether that passage still runs intact beneath the tarmac, has partially collapsed, or was simply misidentified at the time, is not currently known.