A four hour ring drive with no stops, 8-10 hrs. with stops, a day trip is highly recommended. One of the most spectacular places on planet earth. Stops to consider: Kenmare, Rossbeigh Strand, Kerry Cliffs (obviously), Valentia Island, Ballinskelligs Beach, and many more. If you're feeling adventurous, Skellig Michael is worth a look...
Start at Kate Kearney's Cottage, a bike, a walk, or a jaunting car will take you through one of the most famous sites in Ireland. Cut from glaciers (merely) 25,000 years ago, the Gap of Dunloe separates the MacGillycuddy's Reeks and its highest-in-Ireland peaks from the Purple Mountains, so-named from its sandstone purplish hue. Again... spectacular.