The Black Fort (Dún Dúchathair) is a promontory fort closer to Kilronan than Dún Aonghasa — closer to the ferry pier, in fact — but far less visited. Its walls run across a headland above the sea, cutting off the promontory from the rest of the island. The clifftop setting is as dramatically exposed as anything on Inis Mór, and the near-total absence of other visitors gives it a quality that Dún Aonghasa, magnificent as it is, cannot match in summer.
The walk from the road takes about 20 minutes on a marked path across limestone pavement. There is no entry fee. The fort's walls are in reasonable condition and give a real sense of the scale of the original construction — large blocks of dry-laid stone, fitted without mortar, still standing after more than two thousand years.