Dún Aonghasa

Dún Aonghasa (Dun Aengus) is the largest and most dramatic of the prehistoric stone forts of the Aran Islands, set on the cliff edge on the south coast of Inis Mór. The fort is built hard against a sheer drop of around 100 metres into the Atlantic, its semicircular plan using the cliff itself as the fourth wall. It was first built around 1100 BC and re-fortified in the early medieval period (roughly 700–800 AD), and consists of three massive concentric dry-stone enclosures.

The most striking defensive feature is the chevaux-de-frise — a wide band of jagged limestone slabs set upright in the ground around the fort, designed to break up and slow any attacking force long before it reached the walls. Excavations inside the innermost enclosure have found evidence of Bronze Age dwellings and metalworking. Why a structure on this scale was raised on the edge of the known world is still debated: defensive stronghold, ceremonial site, or a statement of power over the Atlantic approaches.

Access is via the OPW visitor centre at Kilmurvey, from which a 1 km uphill path over bare limestone leads to the fort (about 15 minutes; not suitable for wheelchairs or poor mobility). There are no railings or barriers at the cliff edge — the drop is sheer and the Atlantic wind can be ferocious, so keep well back, especially with children. Most visitors reach Inis Mór by ferry from Rossaveel (about 40 minutes) and cover the 7 km from Kilronan pier by bike, minibus or pony trap. Allow a full day for the island.