To the ancient Hawaiians, it was the House of the Sun, where the demigod Maui lassoed the sun to slow its path and give his mother more time to dry her tapa cloth. But to modern visitors, Haleakala -- Maui's massive dormant volcano -- is a bizarre moonscape of cinder cones nearly two miles above the beaches.

For years, people have been seeing Haleakala (pronounced Holly-ahk-ala) by helicoptering over it, hiking or horse-trekking into it. Now there's an entirely different way to get to know it -- bicycling down its slopes from the 10,023-foot summit to the sea.

Not long ago I found myself -- with 14 other riders -- straddling a modified mountain bike next to the volcano's highest observation point, preparing to coast down. It had been ages since I had been cycling, and I looked apprehensively down the mountain, remembering that we would be going 38 miles on the steepest road in the world (no other descends so far in so short a distance).

Cruiser Bob's Haleakala Downhill originated these bike trips down the volcano in 1983 and offers them three times a day year-round. On the way up in the van -- the bikes in tow behind in a trailer -- guides Tom and Bear made the volcano seem friendly. They told us a bit of plantation history, explained how pineapples are planted, pointed out some Hawaiian cowboys moving stock. They also showed us where we should be especially attentive on the way down. ("This green house marks the beginning of a mile of rough road.")

The turns got sharper as we left the ranchland and entered the Kula uplands. From its base to the top, the volcano shows a complete range of vegetation. We had traveled from rich farm areas to where the slopes were covered only with tough scrub, brown grass and clusters of hardy evergreen trees.

Two-thirds of the way up the volcano we entered the Haleakala National Park, and stopped at park headquarters for a break. Inside the building are maps, photos and restrooms.

Back on our ascent (which took about an hour and a half from Cruiser Bob's cycle shop in Paia to the top) Tom outlined safety information, explaining how he would lead us in single file and Bear would follow in the van, preventing cars from passing until we could all move over to the side. He told us about the bikes' heavy-duty brakes, and cautioned which curves were sharper.

The fact that we were now so high that all we saw was a bleak landscape of reddish-brown cinders, with larger pumice boulders erratically strewn about, underscored the importance of his safety instructions. As a postscript he added cheerfully, "The volcano has not erupted for more than 200 years, but if it should go today, just forget everything I told you, and I'll meet you at the bottom."

The cold air on the summit was a shock: It's sometimes 30 degrees colder atop Haleakala than at its base. A sign near the observation lookout read "Walk slowly at this altitude."

While Tom and Bear unloaded bikes from the trailer and adjusted seats for those who needed it, we had a few minutes to look at the crater. It's worth driving up just to look at the enormous volcanic basin, 21 miles across. The island of Manhattan could fit into it, with none of the buildings rising above the rim.

The crater has a hundred different moods, depending on the weather, but all seem other-worldly, as the light changes on the rust, brown and ochre cinder cones. Clouds creep up the outer sides and waft into it around midday, eventually obscuring the entire crater, except for odd shafts of light moving about like playful spotlights.

Tom offered gloves and candy bars as we mounted our bikes and drew into a single line. When we were ready, Tom shouted, "All right, roll 'em" -- as if we were a westbound wagon train pulling out. I took a deep breath, tested the brakes twice more and moved off, thinking, "I can't believe I'm doing this."

We only went half a mile, to the crater overlook parking lot, to make sure everyone's gear was in order, and that everyone still wanted to continue. It was, and we did.

As we set out again, all I thought about was the bike -- how steady it was, how responsive its brakes, how close I was to the excited teen-age boy in front of me. In a few minutes though, I realized I was very cold. My ears and nose seemed quite frozen by the wind. My eyes watered.

I knew my arms were too tense going through the steeply banked curves, because I was still somewhat edgy. I practiced braking slowly approaching the curve, then releasing to gain speed in it, just like driving. On each curve I gathered confidence, and my sensory awareness increased. The road was so smooth, the wide bike tires just hissed, but the wind flapped my windbreaker noisily around my ears.

Before long I was able to take my eyes off the road for split seconds -- to glance at the line of blue-jacketed cyclists bending around tight turns, or to look out at the clouds below us caressing the cinder slopes. We were cruising at about 25 miles an hour, but it seemed like 65, and it grew more and more thrilling.

Tom signalled us to pull over occasionally, when Bear (in the van behind) told him by radio that cars were backing up. After they passed, we eagerly took to the road again, tackling the switchbacks with elan. Occasionally we'd enter a cloud, which would drop the temperature sharply and put a fine mist on my sunglasses.

After a brief stop at park headquarters, I noticed the air on my face warming appreciably, and I began to smell more of the volcano's plant life -- the tangy scent of pines, the whiff of a carnation farm in Kula, a eucalyptus grove.

By the time we stopped for a picnic lunch, everyone was completely at ease with the bikes and each other. It was so much warmer, most of us stripped down to T-shirts before heading out again.

At lower elevations, the road was not so steep. I leaned down over the handlebars to keep up the speed I'd found so exhilarating above. I laughed at foolish cattle galloping away from us in alarm, and again at the pleasure of seeing homes with hibiscus hedges and plumeria and flame trees awash in yellow, white and red blossoms. I was singing as we came into sugar cane areas, where a hot wind from the sea kept us moving.

Finally, 2 1/2 hours and 38 miles after we left Haleakala's summit, we arrived in seaside Paia, with all the tourists on the sidewalks staring as our chorus of bells rang out. I had mixed feelings pulling into the bike yard, glad we were down safely, but sad to see it end.