The Na Pali Coast is rated by National Geographic as one of the wonders of the world. It's indescribable how stunning it is! We recommend either taking a boat tour (which will take you through the sea caves) or seeing it from the air in a helicopter. Both are 100% worth the money!
Referred to as the "Grand Canyon of the Pacific", Waimea Canyon State Park is insanely gorgeous. And near our wedding venue! After driving the winding road up into the canyon, there are tons of different lookouts and short hikes to do. We recommend doing the whole drive. It's completely doable in a day.
There are tons of amazing beaches all around Kauai. You can always catch a good sunset at Poipu Beach or Salt Pond Beach on the south side of the island. If you're on the north side, Hanalei Bay is surrounded by mountains and waterfalls. One of our favorites is Polihale (shown in the photo above), but it requires driving about an hour along a bumpy gravel road.
Kauai is one of the wettest places in the world. That means tons of waterfalls. If you drive up into Waimea Canyon, you'll get a view of the beautiful Waipo'o Falls. Near the airport, Wailua Falls is a gorgeous cascading waterfall right off the side of the road (shown in the image above). Other waterfalls that are accessible include views of Opaeka'a Falls, a short hike to Ho'opi'i Falls, or a full-day hike to Hanakapiai on the north shore of Kauai.