Dún Aengus Hillfort is the main draw to Inis Mór, the largest and most populated of Aran's three islands. Stretching more than 16 km (10 miles) long and about 2 km (1 mile) wide at most points, with an area of 7,640 acres, it's too large to fully explore on foot on a day trip, so hire a bicycle near the pier to navigate its lanes.
If time permits, head for the less frequented west of the island, visiting Dún Dúchathair, a dramatically sited, freely accessible promontory fort.