As much as I love Hawaii after my six visits, I do find a certain sameness to the usual tourist haunts. 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 day at the beach. 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 desert 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.

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, tropicality 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 bizarre succulents and mutant ferns.

"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 long had 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, riding out of the clouds that often blanket the higher reaches. They pay to be shuttled up the road to almost 10,000 feet, then mount their bikes and ride all the way down, 38 miles of wheeeeeee.

Over on the eastern edge of the park, overlooking the infinite Pacific, the cliff-hugging, twisting 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 photos of the endless crater floor (or, looking the other way on clear days, of Lanai and Molokai far out on the western horizon).

KRISTIN JACKSON / THE SEATTLE TIMES The silversword plant grows in the harsh high elevation of Haleakala volcanic crater on the Hawaiian island of Maui.

But those are the easy ways to do Haleakala. 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 lead down 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.

Wild stuff

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 one of the world's largest dormant volcano.

When my 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 5 feet high out of its middle. 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 woodstove and strolled out to watch the sunset, a proper flock was scratching around the yard.

There's another cool Hawaiian touchstone in Haleakala: the lava tube. A big one opens up about a thousand yards from the cabin. We scrambled down into the spooky lava cave, flashlights in hand. . The tunnel was wide, echo-laden and, once we got a hundred yards in and doused our lights, absolutely black 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.

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.