Seeing Na Pali From The North Shore
In Kauai, the prime attraction is the Na Pali Coastline. It's simply breathtaking. While it is possible to hike much of it, you gotta see it from the ocean in order to truly do it justice. All year, Na Pali catamaran and zodiac raft tours leave from Port Allen and Waimea. They do a fine job but usually don't visit the last couple of miles of Na Pali due to high surf. They have a much better chance of making it in the summer time though.
Also during the summer, you can depart from Na Pali and you are guaranteed to see the entire coastline. Thats because the start much closer to Na Pali than Port Allen and even Waimea. Tours from north shore include snorkeling and most can go inside all the sea caves. It can get rough on the way back up, even in the summer so this is for the adventures.