Beneath the inner edge of the southern bank runs a souterrain, an underground stone-built passage or series of passages of the kind that Early Medieval communities constructed for storage, refuge, or concealment. This one is at least nine metres long, divided into two passages connected by a low, narrow creepway, and it extends across what may have been the original entrance to the enclosure above it. That a hidden underground structure should sit directly beneath a possible threshold is the kind of detail that invites more questions than the surviving archaeology can answer.

The rath itself, a univallate ringfort meaning one enclosed by a single bank and ditch, sits on fairly level ground about 150 metres west of the Finglas river. Its roughly circular interior measures approximately 26.6 metres across one axis and 28 metres across another. The earthen bank survives well for most of its circumference, standing up to 1.6 metres high on the inside and 2.4 metres on the outside, though the eastern sector has been levelled and replaced by a drystone-faced scarp incorporated into the field boundary system at some later point. The external fosse, the ditch that runs outside the bank, is best preserved on the western side, where it reaches 2.4 metres wide at the base and around a metre deep; on the eastern side it has been disrupted by field fences and a drain. There are two breaks in the bank, one at the north and one at the south, measuring four metres and 1.4 metres wide respectively, but which of these represents the original entrance is not known. The souterrain described by J. Cuppage in the 1986 Dingle Peninsula archaeological survey is in a mixed state of preservation. The western half of the structure has lost its roof and its passage averages less than 0.7 metres in width. The eastern half is blocked by collapse, though a gap beneath one roof-slab allows a partial view of the creepway beyond. A separate drystone passage, located in a depression about six metres to the north, is filled almost to its roof but runs southward for at least three metres and is thought to connect with the main system.