Killary Fjord is the reason Leenane feels larger than its size. The flooded glacial valley runs inland from the Atlantic, with County Galway on one shore and County Mayo on the other, and the mountains pinching the water into a long, dark corridor.
You can enjoy it from the road, but a boat trip gives the fjord better scale. Watch for mussel lines, waterfalls after rain, and the way the slopes change colour when the cloud breaks.