Galaway & the West of Ireland Trip: 5/31/2017-6/6/2017. Dun Aengus is the most famous of several prehistoric forts on the Aran Island of co. Galway, Ireland. It is located on Inishmore at the edge of a 100 meter high cliff. Dun Aengus is an important archeological site that also offers a spectacular view. It was built during the Bronze Age and dates from 1,000 BC or before. It has been called the “most magnificent barbaric monument in Europe”. The name Dun Aengus means Fort of Aengus and refers to the pre-Christian god of the same name described in Irish mythology.