Instead of running in the straight lines that generations of agricultural improvement imposed on the Irish countryside, it curves. The arc follows a logic that has nothing to do with modern farming, tracing out a sub-circular shape roughly 60 metres east to west and 42 metres north to south, part stone-built wall and part grass-covered earthen bank, the whole thing sitting on a gentle eastward-facing slope as though it simply grew there.

This is an enclosure, a category of monument that turns up across Ireland in considerable variety but is often passed over in favour of more dramatic survivals. The boundary here combines two distinct forms of construction: a stone-built field fence rising to around 1.5 metres along the western to south-eastern arc, and a lower earthen bank, roughly 0.7 metres high, completing the circuit elsewhere. The bank makes a right angle to the south, an unusually deliberate geometrical feature for what might otherwise look like a natural rise in the ground, and it breaks at two points, to the south-east and to the north. Those gaps, combined with the near-circular plan, suggest this was never simply a field wall thrown up for livestock. Enclosures of this type in Cork and across Munster are frequently associated with early medieval settlement, the rounded form echoing the classic ringfort or rath, a farmstead type in use roughly between the fifth and twelfth centuries, in which a family and their animals sheltered within a defined, banked boundary. Whether Coolabaun's enclosure served a domestic, agricultural, or ritual purpose remains unresolved.