The island of Kauai has 43 gorgeous white sand beaches, stretching over 50 miles, more beach per mile than any other island in Hawaii! Poipu Beach is the beach lover’s beach on the South shore, right outside the doors of the Sheraton-Kauai. Swim, snorkel, boogie board, or find some turtles in the tide pools.
6 of Hawaii’s top golf courses are located on Kauai. 3 of them are in or nearby Poipu: the Poipu Bay Golf Course, Kiahuna Golf Club and Puakea Golf Course. Green fees range from discount to resort, but even the most expensive offer some specials when you purchase multiple rounds.
ATV’s + Hawaii = Awesome.
Catamaran tours of the Na Pali Coast are highly recommended with a visit to Kauai! There are numerous companies based in South Kauai, though Captain Andy's has the highest reviews. Take your pick of one of their many options, from daytime snorkel adventures, to up-close dolphin/whale tours, to scenic sunset dinner cruises!
There are TONS of beautiful hikes around Kauai. Jungles, waterfalls, caves...you can find them all. Check out the above website for some ideas. The Mahaulepu Heritage Trail is based from Poipu Beach, and is a 4-mile hike with relatively easy terrain. For those of you looking for more of a challenge (and extra beautiful scenery!), consider conquering the Kalalau or Hanakapial Trails.
Much of beautiful Kauai can only be seen by air. Many helicopter tours are available, though the Jack Harter Helicopters have the top reviews.
For more pre-trip planning, check out this website: http://www.hawaii-guide.com/kauai/kauai-must-see-and-do