This is a souterrain, a type of underground passage found at early medieval Irish settlement sites, generally thought to have served for storage, refuge, or both. What makes this one quietly compelling is the way it exists in a kind of interrupted state: a modern access point has broken open its middle section, exposing the interior, while the rest of the passage continues in both directions, partly sealed, partly collapsed, partly swallowed by vegetation.

The visible length of the souterrain runs to approximately 6.4 metres in total, oriented roughly north to south within the northern half of the cashel's interior. A cashel is a ringfort built from stone rather than earthen banks, and this one likely dates to the early medieval period, when such enclosed farmsteads were common across the Irish landscape. To the north of the access point, the passage survives in relatively good condition: around 3.4 metres long, 1.2 metres wide, and only 0.75 metres high, its walls corbelled slightly inward and covered by flat lintels. Writing in 1933, a researcher named Wallace recorded the walls as standing three or four courses high and noted that a large flat slab closed off the northern end of the passage. To the south, two intentionally placed stones block most of the route, though the passage can still be traced a further 1.4 metres beyond them before it turns southeast and meets a scatter of collapsed stone. Above ground, the line of the souterrain can be followed another two metres or so to the southeast, after which rubble and dense vegetation take over entirely.

The deliberate blocking stones are particularly worth noting. Souterrains sometimes incorporated such features by design, and their presence here hints that whoever built or later modified this passage had specific intentions about controlling movement through it, whether for security or simply to seal a section no longer in use.