Many locals pick this ruined ancient fort, dating from the Iron Age or early medieval period, as their favourite Inishmore historic sight. It's dramatically perched on a clifftop promontory 2km southwest of Kilronan with terraced walls up to 6m high surrounding the remains of a clochán (early Christian beehive-shaped hut). Its name, meaning the Black Fort, comes from the dark limestone prevalent on this part of the island.