Go on a guided hike through Kokee State Park (808/335-9975; kokee.org), which borders 3,587-foot-deep Waimea Canyon, and see why its twisting dales and rock formations inspired Mark Twain to call it the Grand Canyon of the Pacific. For a more subdued encounter with nature, try Allerton Gardens (808/742-2623; ntbg.org), with 100 sea-cliff acres and 268 species of rare native plants.
The six-acre Kahuna Valley (808/822-4268; kahunavalley.org; doubles from $159) retreat draws healing masters from around the globe to teach Qigong, Taoism, Reiki, and Hawaiian Kahuna healing. At the spa, choose from hot-stone therapy, deep-tissue massage, or a starlit watsu session with mineral-rich waters from the nearby Makaleha Mountains.
Specializing in lavish private house rentals on the North Shore, Pure Kauai (866/457-7873; purekauai.com; four nights from $3,000 per person, double) is all about pampering. Your dedicated concierge will arrange everything from a beachfront luau to sunrise yoga or private surf lessons. The Grand Hyatt Kauai Resort & Spa (808/742-1234; kauai.hyatt.com; doubles from $430) unveils a 20,000-square-foot addition to its Polynesian-inspired Anara Spa—book an open-air hale for a lomilomi rubdown.
It's impossible to drive the roadless, 11-mile Napali Coast; instead, take in the dramatic 3,000-foot oceanfront cliffs from the sea. Since 1980, Capt. Andy's Sailing (808/335-6833; napali.com; $139 per person for five hours) has been navigating Napali's waters—home to humpback whales, spinner dolphins, and endangered sea turtles. On the North Shore, test your adrenaline threshold on horseback treks, Zodiac boat rides, and ziplining at the Princeville Resort (808/826-9644; princevillehotelhawaii.com; doubles from $500).
With Outfitters Kauai (888/742-9887; outfitterskauai.com; $98 per person), you'll be river kayaking through mangroves en route to hidden swimming holes. End the day with a covered wagon ride across landscapes you may recognize from Jurassic Park. Kiahuna Plantation & The Beach Bungalows (800/367-5004; castleresorts.com; cottages from $260) is like summer camp; its 35 oceanfront acres are ideal for picnics and pickup croquet games.