The Big Island has size on its side, not to mention fun volcanoes. Oahu has the storied North Shore. And Maui—well, let's just say that the honeymooners storming its beaches year after year don't come for nothing.

But little Kauai has it all: lush greenery, volcanoes, small towns not yet overrun, and a seemingly endless supply of hidden beaches for surfing, snorkeling, and sunbathing.

This year, all those options are more accessible than ever. On the island's north shore, the St. Regis Princeville opened its doors last October (doubles from $385; stregisprinceville.com); after taking over the historic Princeville Resort, St. Regis revamped the whole place with a classy retro look. (Think coconut palm floors and a new spa and restaurant by über-chef Jean-Georges Vongerichten.)

But you don't go to Kauai to lounge. Join the locals for stand-up paddleboarding in Hanalei Bay—there's a great SUP surf break by the Hanalei Pier—or along the flat calm of the Hanalei River. Kayak Kauai offers lessons and boards (rentals from $42 per day; kayakkauai.com). In the nearby Hanalei National Wildlife Refuge, a coastal wetlands teeming with endemic bird species, you'll find the Okolehao trail—a windy, two-mile path offering views of Hanalei Bay and the mind-blowing Na Pali coastline. If it's surf you're after, head 45 minutes south to Poipu, rent a board at Nukumoi Surf Co. ($6 per hour; nukumoi.com), and try the Poipu Beach surf break, one of the island's best. Afterwards, crash just 50 yards away at the year-old Koa Kea, the first and only boutique property here (doubles from $299; koakea.com).