The place that impressed me most was the Cliffs of Moher. I was overwhelmed by the force of the elements as the wind and sea slammed into the coast. Imagine-- winds that blew all the way across the Atlantic, with nothing to break their force. It was Nature as you rarely get a chance to see it. If you can be there when the sun is out, don't miss it. And you'd be near the Burren, so go there, too.