Inishturk is a proper island day out from the Westport side of Mayo, reached by ferry from Roonagh rather than by impulse. The island is small, sparsely populated, and exposed to the Atlantic, with cliffs, old field patterns, archaeological remains, and views that run toward Achill, Clare Island, and Connemara.
Go because you want slowness, walking, and weather, not because you expect a packaged attraction. Ferry times control the day, and conditions can be blunt, but that is exactly what gives Inishturk its edge.