Dún Dúchathair, Stone fort on Inishmore cliffs, Aran Islands, Ireland.

Dún Dúchathair is a large stone promontory fort on a limestone headland at Cill Éinne (Killeany) at the eastern end of Inishmore, County Galway, about two kilometres from Cill Rónáin. A dry-stone wall roughly 70 metres long, standing five to six metres high in three terraces, cuts the headland off from the mainland. Inside are the remains of oval and elongated clocháns, and outside the wall traces of a cheval de frise.

Its age is unknown; the sources record no construction date. It is one of seven stone forts on the Aran Islands, and it may be considerably older than the better-known Dún Aonghasa, which has drawn more attention from scholars. The fort lies on the landspit Dúnach Ard, partly undermined by the sea, and was cut off from the mainland by a dry-stone wall about 70 m long.

Within the fort's walls stand the ruins of clocháns, traditional beehive-shaped stone huts that demonstrate ancient Irish building techniques and reflect the resourcefulness of early island communities in creating shelter and storage spaces.

Visitors can reach Dún Dúchathair by ferry from Rossaveal or Doolin to Inishmore, then travel across the island by bicycle, bus, or horse-drawn carriage, with no entrance fee required for exploring the site.

The fort features a cheval de frise defensive arrangement of sharp stones positioned at angles outside its entrance, designed specifically to prevent attackers on foot or horseback from approaching the fortified walls easily.