You can take the "Seafari" trailer from Kenmare itself, but it won't take you as close as a local fisherman in his small fishingboat. There is a small harbour, not far from Clooney Loughs and Tuosist village, where a (Dutch) former fisherman offered sealwatching and fishing trips when we were there. Hope he's still around, he also had great stories!
It's great to watch them at this short range!
The mountain scenery, the waterfall, the lakes, the views....
And of course the stone circles and other ancient monuments are really a must! There are scores of them on Beara, but it's nothing to compare with Stonehenge (if you like such busy places) - just a field, sometimes hard to find, with a rusty tin to put in coins as "entrance fee"!
..on the weather, but also on the area underfoot of where you're going. Below the thick growth of ferns and blackberries can be moorland with wet and soft underground, a hidden stream, or some sharp rocks. Good shoes and some experience in mountainhiking can be helpful!
And don't forget map, compass, a good coat or cover, as sudden rainshowers or seemist can drift inland unexpected!