Ballybun(n)ion.

There's not a lot left of the castle at Ballybunion.
It's been around since 1500 or so, but even as recently as 1998 was struck by lightning which took quite a chunk off it (here's how it looked before that).
The cliff walk which starts on the promontory along from the castle is pretty spectacular, especially on a windy winter's day like today. It goes from Men's beach, past Ladies (sic) beach, Nine Daughters Hole, the Virgin Rock to the inaccessible Nun's beach.