Hawaii's Haleakala. After witnessing what Mark Twain called `the sublimest spectacle' he'd ever seen, we descended from frosty, barren peaks to temperate grasslands, through what is known as `Biker's Paradise'

THE good news is that it's a bike ride. The bad news is that it's 38.2 miles long. The great news is that it's all downhill. The worst news is that you have to get up at about 2 a.m. The best news of all is that it's worth it!

Mt. Haleakala, ``the House of the Sun,'' is a broad, brooding dormant volcano rising 10,023 feet above the sea and dominating Maui, second-largest of the Hawaiian Islands chain.

The view from the summit on a clear day and at sunset is spectacular. But the best view, we were assured as we staggered sleepy-eyed aboard the minibus that was to carry us to the top, was at sunrise. A sight that moved Mark Twain to exclaim, ``It is the sublimest spectacle I ever witnessed.''

It was from the summit of this largest dormant volcano in the world that our bike ride was to begin.

Eleven of us sat in the bus, jostling along as our cheerful guide, Deedee Pachico, gave a nonstop narration of what we were driving past during the inky 3-hour drive above the clouds.

``Most of the vegetation we're passing has been imported,'' Deedee said as we swept past fields of sugar cane and pineapples. ``Only above 7,000 feet are the plants indigenous, including the rare silversword. I know it's too dark to see anything, but you'll get to see it all on the way down.''

At the summit we jumped off the bus and promptly jumped back on board. Somehow you don't expect to freeze on Maui, even at this altitude, but the temperature had dropped to 34 degrees, and the wind whirled around, adding to the chill.

Hooded yellow nylon windbreakers, baggy matching pants, and black helmets made us look like a bunch of extras from the set of ``Star Trek IV'' but helped stave off the biting cold. With the planet Venus as our major light source, we edged slowly and carefully to the rim of Haleakala, as sheets of tiny silvery ice crystals crackled under foot.

Here we waited patiently for the mythical demigod Maui's promise to be fulfilled. It was Maui, according to legend, who snared the sun in its journey across the sky and held it until it promised to travel more slowly over these verdant Pacific isles.

Dawn finally arrived wondrously as the sun broke with a flash across the blanket of clouds, lining them with a thin edge of gold. In a few minutes the mouth of this great volcano lit up before us - a crater so vast that it could swallow Manhattan Island!

Soon the light turned the sky to soft hues of golden pink and revealed a desolate, lunar landscape. If not the ``sublimest spectacle'' we had ever witnessed, it did bring a few more goose bumps to our arms.

Anyway, there was no time to linger and wax poetic. Back at the parking lot, our bikes were waiting, and the long black asphalt road stretched like a ribbon before us.

``OK, gang! Grab a bike and take a practice spin around the parking lot, and let's go. We've got a three-hour ride ahead of us,'' Deedee shouted above the howling wind.

I picked out a Diamondback Sand Streaker bike with Cantilever brake system.

We went over the rules of the road: Don't pass anyone; don't look around; stay 25 feet apart; no freewheeling; stay to the right, etc.

``If you break the rules or if you can't keep up, it's back in the bus,'' Deedee warned.

And down we went, slowly at first, from the frosty, barren peaks through more temperate grassy cattle country, around hairpin turns and stopping for an occasional picture. Great stands of eucalyptus trees along the road gave off the heady smell of spice as we passed beneath them.

Deedee, always in control, was in constant telecommunication with our bus driver, who followed watchfully. If anyone fell out of line, Deedee was quickly informed.

At 10 miles we made a pit stop at a visitor center. There we got a close look at the silversword plants and nenegeese. The silverswords, once common here, are now rare and protected. Not many years ago it was considered great sport to uproot them and roll them down the mountain. It was little known then that it takes seven to 30 years for a single plant to mature, bloom, and die. Only then does it cast off its seeds.

Unfortunately, cattle, sheep, and feral goats and pigs brought in by early settlers acquired a taste for the young plants.

Nene geese, Hawaii's national bird, haven't fared any better. They have been moved to this higher, protected area to save them from extinction. As part of the process of adapting, they have begun to develop short claws on their webbed feet to help them climb the rough terrain.

Back on our bikes, we continued our descent with greater speed and confidence.

``There are 29 180-degree turns in the next 13 miles,'' said Deedee. ``It's called `Bikers' Paradise.' Let's go!'' (You'll find everything good on these islands referred to as ``paradise.'')

We zipped through the zigzag turns and finished the trip through flat fields of sugar cane and pineapples in fine fettle.

A breakfast of eggs Benedict, French toast, or fritatta was laid out and waiting in the little town of Makawao.

``I did it! I did it!'' one older woman from Michigan exclaimed as she pulled off her helmet. ``Now I have something to tell the girls at bridge!''

``It was like traveling through three different countries: arctic, temperate, and tropical,'' said one of the male members of the party.

``I loved the smells and the scenery,'' said another, and she added, ``I'd like to back up and do it all over again.'' Practical information:

Three companies offer bike rides down from Mt. Haleakala. Each charges about $75, including a pickup at your hotel. Continental breakfast and lunch are also included.

The companies are listed in the free brochures available at hotels, condominiums, and rental car agencies on the island.

Later morning and afternoon trips are available daily. All excursions are limited to around 14 people, so book early.

Dress warmly. A heavy sweater or light jacket is a good idea. The windbreakers that are provided aren't enough. As you descend, clothes may be shed.

Binoculars and sun glasses are not essential, but you might find them worth carrying.