Rain can put a damper on your Kauai vacation, but you can (almost) always find sunshine and blue skies on the arid south coast—at the resort strip of Poipu Beach. But Poipu is not all arid and beach: Two of the nation's five National Tropical Botanical Gardens are here, including Allerton Garden (where TV's Fantasy Island was filmed, along with several movies) and the sprawling McBryde Garden (above). The gardens have a visitor center, with no admission charged, that offers a third choice if you don't have time to visit the main attractions.
Across the highway from the visitor center is Spouting Horn, where busloads of tourists arrive to watch seawater blast geyser-like from a hole in the reef. A garden trail skirts the coast from here for a half-mile, to the entrance gate to Allerton.
The resort strip of Poipu, anchored by the Sheraton, is not as crowded as others in the Islands, though it gets jammed up on weekends. Poipu Beach Park on the east end of the strip is a family fave. Snorkeling and surfing are both good. Hawaiian monk seals (an endangered species) often haul out to sunbathe amid sunburned visitors.
A short walk from Poipu gets you to one of the best destination resorts in the world, the Grand Hyatt Kauai. A man-made saltwater lagoon sits just inland from the ocean, and a Disney-esque pool is a few steps away.
From the top of Makawehi Bluff at the Hyatt is a view of Shipwreck Beach, popular among local surfers. People jump from the bluff. Saner people embark on the Mahaulepu Heritage Trail, which begins here. Wildlife, sesacapes, and ancient sites highlight the sandy route.
After about a mile, the Heritage Trails drops down to Mahaulepu Beach, where kayaking, paddle boarding, and snorkeling are options. You can also drive here from the Hyatt, via a hellishly potholed road.
From Mahulepu, the trail continues for another mile to Haula Beach, a wild beauty. For more details, check out Kauai Trailblazer. A lot of fun stuff is hiding in plain sight.