This is Mullaghdearg beach, Co. Donegal.
I spent every summer on this beach as a child, though it can be dangerous for swimming further out due to strong currents.
“A truly breathtaking beach, Mullaghderg is located in between Kincasslagh and Annagary. During the late sixteenth century a vessel from the Spanish Armada was wrecked just off this beach whilst trying to return home through the North Atlantic. In more recent years Mullaghderg was a site of a massive tragedy when an old World War 2 German mine washed ashore. A group of people gathered around it to check it out. The mine exploded killing about 19 people from this area.”