The circular outline, once mapped on the second edition of the Ordnance Survey, has been reduced to a faint arc in a field boundary running northwest to southeast, a very low earthen bank, and the slightest trace of an external fosse, the shallow ditch that would once have ringed the outer edge of the enclosure. That fosse is actually the telling detail here: it places the site in the category of a rath rather than a cashel. A cashel is defined by a stone wall, whereas a rath is an earthen ringfort, and the presence of a fosse is characteristic of the latter. The enclosure measures roughly 32 metres across, a modest but not unusual size for an early Irish farmstead of this type.

The more remarkable discovery came not from careful excavation but from the mundane work of levelling the site, which happened some years before J. Cuppage documented the area in the 1986 Dingle Peninsula archaeological survey. During that levelling, a souterrain was uncovered beneath the ground surface. Souterrains are underground stone-built passages and chambers associated with ringforts throughout Ireland, most likely used for storage or refuge. The one at Dún Sheáin consisted of a passage built from upright stone slabs and roofed with flat lintels, leading to at least two chambers described locally as resembling underground beehive huts, each sealed by a single flat roofing slab. One of the entrances was formed by a porthole slab, a large stone with a rounded or shaped opening cut through it, just wide enough to admit a person. It is a feature found in other Kerry souterrains and lends the structure a quietly purposeful quality, as though its builders were thinking as much about who might need to move through it quickly as about how long it might stand.