Fodor's Expert Review Dún Aengus

Even if you have only a few hours to explore Inis Mór, rent a bike (next to the pier) and head straight for Dún Aengus (or Dún Aonghasa.) Set at the edge of a 300-foot precipice towering over the ocean, this semicircular fortress is one of the finest prehistoric monuments in Europe and the main draw to Inis Mór. The purpose of its construction more than 3,000 years ago is a matter of conjecture, and also irrelevant to the legions of seabirds who occupy its scenic Atlantic perch looking out on Connemara and the 12 Pin Mountains. Beware: there is no barrier to the 300-foot drop at the edge. Allow 1–1½ hours for a visit.

In order to protect this fragile monument from erosion, you should approach it only through the visitor center, which gives access to a 1-km (½-mile) uphill walk over uneven terrain—wear sturdy footwear.