"This is the last place to turn around. Beyond here, we're committed."

As the sun beats down and the ocean swells lift our bright yellow sea kayaks, our guide points his paddle at the end of Kee Beach on the northern shore of Kauai.

Beyond, the jagged green ridges that form the Na Pali Coast -- famous backdrop for movies from "Raiders of the Lost Ark" to "Jurassic Park" -- plunge into the sea for 16 miles to our final destination. My girlfriend and I consider ourselves active types, but this is farther than either of us has ever paddled.

"Anyone? Last chance to bail."

During the pre-dawn drive to the beach this morning, the two guides had advised our group of 10 that seasickness could be a serious issue and that anyone so inclined should "take one for the team" -- meaning an extra Dramamine -- just in case. The trip along the island's uninhabited north shore is billed as the adventure of a lifetime and "the Everest of sea kayaking": the roughest and longest one-day sea kayak trip in the world.

The beach looks so inviting, and the open ocean looks so . . . open. A folding chair, a paperback and a drink with a little umbrella in it seem like a good idea right about now. But I keep quiet, and soon we're paddling west in loose formation.

There are two schools of thought when it comes to vacations; call them the "snoozers" and the "shakers." The former incline toward inactivity. Vacations are a time for unwinding, for doing as little as humanly possible, they say, whether you're in Papeete or Peoria.

The others tend to fill the days with activity. You've spent the money, taken the time off, traveled for hours or days to get here -- how can you just sit around and do nothing?

It's hard to find a place where this contrast is as marked as Kauai, the fourth-largest of Hawaii's six major islands. On one hand, you have more beaches per mile of coastline than anywhere else in the island chain, along with plenty of resorts, spas and B&Bs -- albeit low-key versions suiting the more relaxed vibe of the "Garden Island."

On the other, Kauai's rugged topography offers enough adventure sports and outdoor activities to stage a tropical X Games. A visit here, as we will learn, can be a balancing act between basking and bustling, rushing and relaxing, doing and undoing.

Surf Central

Visiting Hawaii without trying to surf is like going to Vail without hitting the slopes. Seven-time world champion Margo Oberg began teaching out of a VW van in the 1970s and opened Kauai's first surf school in 1977.

First-timers start out on land near Poipu Beach on Kauai's south shore. Here instructor Alvin Ganzer demonstrates the right way to stand up on a wave, springing to his feet from a prone paddling position in one fluid motion.

"You've got to keep your okole down," he says, squatting like a baseball catcher with his rear end low and arms outstretched. "Otherwise you'll end up rolling up the car windows" -- he flails his fists frantically and pretends to fall backward -- "or nose-diving."

Soon we're ready to join dozens of would-be shredders, most of whom are in their mid-teens -- half our age -- in the water. It's hard not to feel cool carrying a surfboard down the beach -- unless it's an idiot-proof beginner model, nine feet long and covered with foam rubber for safety. On the plus side, they're stable when floating and therefore easy to sit on while waiting for a wave. They're a step up from the original wooden Hawaiian surfboards, which were 12 feet long and weighed 100 pounds.

The tricky part is knowing when to start paddling like crazy: ideally as the wave crests exactly where you're floating, says Ganzer, standing in chest-high water as we bob.

"Paddle, paddle, paddle!" he yells, as he gives each of our boards a shove at the critical moment, like a father teaching a child to ride a bike. Sometimes five students catch the same foot-high wave, but somehow we each find ourselves standing upright, alone, riding toward shore.

Since a beginner board is as hard to steer as a battleship, each short ride usually ends up on the beach or in knee-high water, where we slowly topple. But the thrill lingers.

So does the sting of salt water in the eyes and the feeling of full-body exhaustion at the end of the afternoon.

"Surfing is 95 percent paddling," Ganzer had warned us, and an hour of surfing feels like an hour of push-ups. That night, we fall asleep at 9 p.m. and sleep for almost 12 hours.

A Grand Canyon

Photographers call the hour before sunset, when colors glow with extra vibrancy, the "golden hour." Kauai, the oldest island in the main Hawaiian group, looks like this all the time, like someone nudged up the saturation on a celestial version of Photoshop.

The best place to appreciate this quality is Waimea Canyon, carved by the river of the same name across the western half of the island. Kauai is 33 miles wide by 25 miles long, and most of its interior is rugged mountains. This concentrates the island's urbanized areas -- only 3 percent of the total -- on the coast.

Waimea is only one of the island's winding canyons, which radiate from its center like bicycle spokes after an accident, but it is by far the most impressive. Mark Twain called the 3,600 foot-deep gorge the "Grand Canyon of the Pacific," and the eroded reddish layers do resemble the Arizona landmark. Dusted with greenery, it looks covered in moss from a distance.

The 18-mile road up the canyon's western edge leads to numerous overlooks, and the colors blaze even under cloudy skies. From the Kalalau Lookout near the end of the road, you can see the impossible tropical turquoise of the Pacific meet the knife-edge mountains of the Na Pali Coast, 3,000 feet below.

The two-mile Honopu Trail leads along one of these ridges. It's tough, steep going through tropical scrub, with many logs to hop and thorny ferns to snag your clothes. But the views of the coastal mountains from the end are astounding, despite the sightseeing helicopters that buzz overhead every 15 minutes. In between, the only sounds are the rustle of the breeze and the rubber-squeak twitter of tropic birds soaring on updrafts.

Back in the town of Waimea, we enjoy a well-earned shave ice, a Hawaiian staple, at JoJo's Clubhouse, said to have the best on the island. The service is slow, but the result, picked from more than 60 flavors, is well worth it: mango, guava and pineapple syrup over shaved ice, with macadamia nut ice cream on the bottom.

Wet, Wet, Wet

Kauai's serrated skyline, sculpted by water, includes the one of wettest spots on Earth: the top of Mount Waialeale (Hawaiian for "rippling waters") in the center of the island, which receives an average of 440 inches of rain -- almost 37 feet -- per year.

Rainfall plus steep terrain equals waterfalls, and many of Kauai's are easily accessible. Kipu Falls is near Lihue, with 5,600 inhabitants the largest town on the island. A five-minute hike along a sugar cane field leads to a 20-foot rock cliff that borders a large natural pool surrounded by tropical vegetation.

There's a definite local vibe to the place. Young guys in swim trunks and flip-flops, Kauai's unofficial uniform, lounge on the rocks near the falls, watching friends climb out onto tree limbs like monkeys to retrieve rope swings.

When I get up the courage to play Tarzan myself, they insist I go first. The knotted rope is thick and rough, at the highest point in its swing, when you let go, the moment of weightlessness seems to last forever. A few seconds of falling is an eternity, and the water is a cold crash back to reality.

Two much larger waterfalls are also a short drive from Lihue. Wailua Falls, a mile or so northwest, is 173 feet from top to bottom, and Opaekaa Falls, west of the town of Wailua, measure 151 feet high. You can hike to the bottom of both to swim in the pools, although the trails are steep and unmaintained. The only ropes in sight are tied between trees to prevent tumbles.

After a few swings at Kipu Falls, we decide that's enough shaking for one day and head to Lydgate State Park near Wailua, one of more than 40 white-sand beaches around the island. Ever since a rough semicircle of boulders was built out from the beach, Lydgate has been one of the most popular places on the island to learn to snorkel. The volcanic rocks keep out the force of the surf but let fish through, and visitors are allowed to feed them.

Without any snacks to offer, we find we're not very popular underwater. A goatfish taps little feelers near its mouth called barbels over the rocks in search of something to eat, and a shy little flounder lies camouflaged on the bottom, its eyes peeking from the sand.

The beach, a short walk away, is nearly deserted. Unable to do nothing quite yet, we compromise on reading guidebooks to decide where to go next. It feels like the first time we've sat still during daylight since we got here three days ago, and it's long overdue.

Hawaiian Treats

Kauai's north shore is a lush, mellow microcosm. It's even wetter and greener than the rest of the island, with an end-of-the-road feel that culminates in the unique profile of the Na Pali Coast. No one is in a hurry here -- people often drive under the speed limit, and every financial transaction takes twice as long as it would back home. At the same time, everyone seems cheerful and friendly, whether it's from living in or just visiting what many would call paradise.

There's plenty to see on the drive there for those wearied by active vacations. The 52-foot Kilauea Lighthouse was built in 1913 on the northernmost tip of the island, fitted with a Fresnel lens that weighed four tons and could be seen 20 miles out to sea. The lens was replaced by a more powerful electric beacon in 1976, and today the lighthouse is a national historic landmark. It anchors a national wildlife refuge, home to great frigate birds, red-footed boobies and the nene, an endemic goose that is Hawaii's state bird.

Five miles south is the 450-acre Guava Kai Plantation, source of half of Hawaii's crop. The sweet yellow-skinned guava (technically a large berry) has three times as much vitamin C as an orange, and is good for treating intestinal upsets. The plant was brought from South America to Hawaii in 1791, where it became the most common wild fruit in the state. About 12 million pounds are harvested by hand here every year.

We do our part to clean up the plate of free samples before heading onward to the town of Hanalei, seven miles from the end of the road that encircles most of the island. "Idyllic" is a word that should be used sparingly, but as a laid-back beach town with great scenery, Hanalei comes close.

At the heart of town, which sits at the foot of steep green hills rising into the mist as if in a Chinese brush painting, seafood restaurants cluster near a small shopping center. Dirt lanes lead past houses on stilts to the beach, and traffic comes to a halt at numerous one-lane bridges, where etiquette dictates you must wait for all oncoming traffic to cross before proceeding. It's a good place to help fight the urge to do something all the time.

We buy fish and corn chowder at the market for dinner, and watch the sun set from our hotel balcony. A boy fishes in the surf below as his father casts a net into the water. Tomorrow is the big paddle, and we want to be rested and ready for a pre-dawn departure.

Sacred Scenery

Two hours into the kayak trip, we've gotten into the groove.

Three-foot swells seem a lot higher from kayak level, but with two people in each bright-yellow boat, working the double-bladed paddles isn't that difficult. After a while, the motion becomes almost hypnotic.

A tailwind doesn't hurt, either. We shudder to think of what paddling into the wind must be like. ("If people bonk [collapse], we paddle them," says Webb. "One guy paid $350 to be taken back by motorboat.") Our guides lead us into caves carved by the ocean, where a group of dolphins passes in a series of smooth gray arcs in the water. Waterfalls spill from hanging valleys overhead. Sea turtles seem to be everywhere.

After an extended lunch break -- the guides packed sandwiches -- at Milolii Beach, we continue past Honopu Valley, which we'd glimpsed from above during our hike out the Honopu trail. Accessible only by water, Honopu Beach is considered one of the most beautiful in Hawaii, if not the Pacific, but landing any sort of craft is forbidden. (Unless you're a Hollywood director, apparently -- the 1976 remake of "King Kong" and 1998's "Six Days Seven Nights" feature scenes shot here.) The valley is sacred to the Hawaiians, who once buried their kings here. The men who buried them, it was said, would then kill themselves to keep the location a secret.

It's another hour to the end of the trip at Polihale State Park. We help load the kayaks onto a trailer behind the pickup van and drive three-quarters of the way back around the island to Hanalei and a well-earned breather. For the moment, though, as we watch a waterfall cascade from a thousand-foot cliff of green near a sea arch the size of a school bus, we're happy to stay in shaker mode a little while longer.

Julian Smith last wrote for Travel about hiking in Sedona, Ariz. For a photo gallery with additional images of Kauai and the surrounding area, go to www.washingtonpost.com/travel.

The Kalalau Valley offers dramatic views of the Na Pali Coast.Kayakers paddle down the Na Pali Coast in Kauai, passing waterfalls, sea turtles and soaring cliffs. At right, beginner surfers practice on land before hitting the waters off Poipu Beach, a popular surfing spot on the south shore. Below, a sign alerting drivers to watch for surfers.