It's hard to radicalize a Hawaiian vacation. Mellow just has too strong a lock on these islands. The metronome palms and Thorazine breeze will have your average refugee from the mainland drooling into his Grisham within an hour. By day four, tourists are zombies in leis, happily stupefied by beauty on the Island of the Brain Dead. That's why we go there, after all, raiding our IRAs and cashing in our miles so Polynesia's velvet grip can squeeze us until we're one mai tai short of a coma.

But even paradise can chafe. Personally, as much as I love Hawaii after my six visits (I have family there), I do find a certain sameness to the usual tourist haunts. C'mon now, Hanauma Bay is a lot like Hanalei Bay is a lot like Ma'alaea Bay, at least to someone who still says Huh-WHY-ee instead of Huh-VY-ee. But like Eskimos who reportedly know 200 words for snow (a linguistic urban myth, by the way), people who live there love to parse the faint differences between one palm-lined cove of pearly white sand and the next palm-lined cove of pearly white sand. "Oh, Pokopoopipai is gorrrrrrgeous!" they'll say. Well, yeah. But isn't that like admiring a particularly efficient Burger King? In Hawaii, faultless beauty is just the local franchise.

So what's a tourist to do when he begins to crave something more invigorating than another 50 ccs of tropical Valium? You can always drink yourself silly at the luau and climb on stage with the hula girls. That's been done, for sure. Or you can sign up for surfing, scuba diving, hang gliding or any of the sweaty Gen-X pursuits that fill the brochure racks at the hotel concierge desk. But even those are sort of de rigueur Hawaii, if you ask me.

Or you can walk into Haleakala Crater for a night or two. It's more Mojave than Maui, and you won't ever mistake this beautifully barren valley -- with plant life fit for Jupiter, camel-ready sand dunes and some still-heaving geology -- for just another patch of island splendor. Paradise it isn't; fascinating, it is.

Crater for a Night

Haleakala is, simultaneously, a national park, an international biosphere reserve and a designated wilderness area. That's a whole lotta protection for a whole lotta hole. In essence, Haleakala is a 30,000-acre gash in the highlands of eastern Maui, tapering down from the 10,000-foot rim at Pu'u 'Ula'ula Summit to the rocky surfline at Kipahulu. At the higher reaches, it's all weirdness and arid desolation, a place where rocket scientists come to test drive their robot vehicles in a correctly cruel setting. But as you descend toward the ocean, topicality resumes its throne in the form of lusher greenery and plunging waterfalls. (The two areas aren't connected by road, but hikers can walk from one to another, progressing through a cavalcade of climate zones).

You can't see more than part of the crater from any one point above, but the view from the summit side is of a vast and otherworldly plain that rolls on without end. It's like some grainy feed from a Mars rover, a crimson panorama of cinder cones and windswept peaks. Huge pastures of curdled lava are locked in frozen flow around yellow cliffs. It seems a poisoned terrain, whole acres without a tuft of green; the plants that do cling to the unforgiving soil are bizarro succulents and mutant ferns. The only thing this set lacks in sci-fi cred is Leonard Nimoy pondering his tricorder and some expendable Starfleet security extra standing by to meet his gruesome alien demise.

"I've been all over Hawaii, and I've never seen anything like this," said Gary Johnson, a pilot who regularly ferries a wealthy California client down to his Hawaiian beach house. A devoted backpacker, Johnson had long been keen to explore what he'd been told was Hawaii's most remote backcountry. I met him on the crater floor, with the late morning sun still chasing the long shadow of the surrounding hills out of the basin. He had camped the night before in a rough and broken field of black lava. Now, he had shouldered his pack for a long 14-mile walk down to the sea and the comforts of a more normal Hawaii. "It's more like the Gobi up here, or a moonscape," he said. "You can see why NASA used this place as a test area."

Haleakala is already a well-known stop on the Maui tourist track. The zigzag highway up to the rim is filled every morning with serpent lines of bicyclists, careening out of the clouds that often blanket the higher reaches. They pay to be shuttled to the top, mount up and ride their brakes all the way down, 38 miles of wheeeeeee. Over on the eastern edge of the park, overlooking the infinite Pacific, the cliff-hugging, nail-biting Hana Highway attracts every tourist with a rental convertible and a dose of Dramamine. And the rim-side visitors centers are often crowded with folks snapping pathetically underpowered photos of the endless crater floor (or, looking the other way on clear days, of Lanai and Molokai far out on the western horizon).

But those are the easy ways to do Haleakala, looking down from on high or riding and driving around its outer slopes. Here's what the locals know: Going into the hole is better. Starting at one of the three visitors centers that ring the rim, a network of marked trails leads to three simple huts, each in a different crater terrain: Holua Cabin is tucked into the scrubland at the base of the western rim; Kapalaoa Cabin is in the middle of the basin, surrounded by cinder fields; Paliku is toward the eastern end, below a rain-forested ridge. Each of them sleeps a dozen overnighters in ranks of built-in bunks and each costs $75 a night for an entire group. (Unless you luck out and get a last-minute cancellation, they take some effort and advance planning to book via a monthly mail-only lottery. See box on Page P5 for details.)

The Descent

My own descent into this unusually fearsome corner of our most mild-mannered state began on the rim, at the head of Sliding Sands Trail. Two of my college-age Honolulu-based nieces, their boyfriends and I set off on the eight-mile hike down to Holua Cabin. (The rest of our group, the aunts and uncles and little kids, were hiking a shorter route down).

At 10,000 feet, there was a very un-Hawaiian chill in the air, and walking uphill was more breathless than it should have been. Fortunately, the trail dropped quickly, stringing around a rank of tall red cinder cones, each silhouetted against an azure Pacific sky, some with their tops blown empty by some prehistoric upheaval or another. Mile by mile, we walked down into the world's largest dormant volcano.

In the distance, I could see a party of horsemen crossing the crater floor at a walk, like a Saharan trading party, pulling a low contrail of hoof dust across the plain. Well above them, we spread out and the only noise above our boot steps was the slow hiss of silence rebounding off the cliffs, the eternal exhale of geology.

When my blonde surfer-girl niece Annie Hiller gave a cry, I looked around to see her pointing off the trail.

"Silversword," she called. Twenty yards from the end of her finger rose a plant that Dr. Seuss could have proudly drafted: a low clump of shimmery light green spears, like an agave covered in hoar frost, with an elaborate spindly and dry trunk soaring five feet high out of its middle. A few days earlier we might have seen the last of the purple flowers that covered the trunk like the great feather standards that Hawaiian royalty were so fond of. The silversword, endemic to Haleakala, is one of the plants that extreme botanists come here to see. Carve an isolated, high-altitude enclave into a tropical latitude and the resident flora and fauna get up to all sorts of evolutionary high jinks.

The crater, for example, is crawling with Hawaii's signature endangered species, the nene goose. I'd been all over the islands but had only once before seen the nene (and then only on a private preserve near Hilo). But when we reached our cabin -- a plain and sturdy bunkhouse affair on a lush grassy field in the rain shadow of a cliff wall -- it was surrounded by nene. At first there were only two of them, but by the time we'd cooked supper on the wood stove and strolled out to watch the sunset, a proper flock of them were scratching around the yard. They are handsome birds, with their Audrey Hepburn necks and marbled black-and-white bodies. But they are opportunistic little scavengers, too, fearless and clearly accustomed to crumbs and other offerings from cabin tenants. By the next day, as they pecked our fingers at the standpipe of water in the yard or tailed us to the outhouse, we had stopped marveling at our luck.

Lava Tube Blackout

There's another cool Hawaiian touchstone in Haleakala: the lava tube. A big one opens up about a thousand yards from the cabin. And, unlike Thurston Lava Tube -- that sanitized, paved, crowded and lighted edition at Volcanoes National Park on the Big Island -- this one is a lava tube unplugged. You're invited -- implicitly, since the place is all but unmarked -- to risk your ankles on the dark and craggy footing and your scalp on the devious outcroppings.

After we scrambled down into a spooky cave, flashlights in hand, it became downright spelunkle-ish. The tunnel was wide, echo-laden and, once we got a hundred yards in and doused our lights, absolutely black black. No amount of time brought a glimmer as we stood thrilled and immobile amid the perils, our hands waving frantically in front of useless eyes.

Lights back on, we picked our way through. Huge chambers appeared on either side and, for the bravest climbers, alternate routes opened through overhead chutes. Where cherry-hot rock had once flowed as a molten underground river, only freaky shapes remained: frozen swirls, lacerating spikes. Here and there, a sort of dripping limestone mold formed with excruciating slowness, the tiny pale buds that would become the stalactites of a future eon.

The grand finale appeared just around the last bend, where the tunnel widened into a grand chamber with a hole blasted through the roof. In the very center of the room, decades of visitors had tossed pebbles and stones, turning a pile of rubble into an informal Himalayan-style shrine to the glory of it all. Through the opening, sunlight poured into the gloom, bathing the shrine in a shaft of white -- an enchanted altar in some once-and-future cathedral.

We climbed out, after our subterranean walk, in time for a sunset spectacle that reminded us that we were, after all, in tropical latitudes. And after another wood-fired dinner, we went back out -- in search of moonlit silverswords, this time -- to stand under a star-stippled sky that made it obvious why there is a major astronomical observatory on the rim of this hole, and why there are plans for a possible second one.

After two nights, our reserved time in the crater was up, and we saddled up for a wet and wearing climb out. At just under four miles, the Halemau'u Trail was half the distance our hike down had been, but -- after a preamble amble across a meadow of yellow wildflowers -- it was a steep switchback route that climbed 1,000 feet up a cliff and straight into a cloud.

We were a soggy and chilled party by the time we topped out on the rim, above the rain and pleasantly at the end of our vigor. We had come on this outer-island side trip to shake up Hawaii's entrenched sunny-and-70s surfside routine. Having done that, we drove off the volcano and headed straight for the beach at Kapalua.

Sometimes you just want to veg, you know?

In Hawaii, sometimes you just need a break from paradise. For those times, visitors can hike around the moonscape of Haleakala National Park in Maui, and even spend the night in a cabin in the crater.To experience a different side of Hawaii, visitors can hike around -- and camp inside -- the Haleakala Crater on Maui.Haleakala Crater boasts some rare vegetation, such as the silversword.