Black-Water Rafting: Not for the Claustrophobic : Visitors can ride inner tubes through New Zealand’s glowworm-lit Waitomo Caves.

You’re floating on your back, propelled inevitably forward by a gentle current, lulled by the profound silence and blackness. You stare up at nothing and listen intently to less; the damp chill is of little significance. Gradually, clusters of stars shift into your field of vision.

It’s not night, however, and these stars are unlike any you’ve seen before. You are, in fact, drifting on an inner tube deep in the bowels of a cave, and the celestial splendor on the cavern ceilings is emanating from galaxies of glowworms.

The latest innovation from the folks Down Under--the people who brought you bungee jumping and jet boating--is called black-water rafting. It takes place underground, with wet suits and headlamps, and is as different from white-water rafting as eight-ball is from billiards. The adventure begins at New Zealand’s Waitomo Caves, a two-hour drive south of Auckland on the road to Rotorua.

Before I left on my trip to New Zealand in December, the beginning of their summer, I had spotted the words “black water rafting” in a guidebook. While other adventures would also be on my agenda, I’d never heard of black-water rafting--which meant that wild horses couldn’t keep me away.

Despite one jump over an underground waterfall that requires some mustering of courage, black-water rafting is actually family fun, far softer adventure than most white-water expeditions. According to cave guides, in the three years that rafting tours have been offered by the Museum of Caves, 16,000 people have glided through Waitomo’s tunnels.

The most daunting aspect of the trip may be climbing into a cold wet suit, which is indeed wet. Participants are then advised to carefully select the right size of “raft,” as Kiwis refer to the tubes. I and my fellow cave-travelers--six men and four women from all over the world--quickly discovered that the rafts are all one size, and that the guides are indefatigable jokesters.

The approach to Ruakuri Cave, the cavern used specifically for the rafting tours, is an easy hike, through rain forest, from a parking lot below the museum. Before entering the cave, we made a practice jump off a wooden platform into a creek, simulating the waterfall we’d encounter inside. Guide Phil Johnston advised each of us to “get a death grip” on the tube and jump as far forward as possible, past the rock that juts six feet out directly beneath the platform and into the water beyond that is a comfortable 20 feet deep.

Then he warned us about “The Blender.”

“At the top of the waterfall,” Johnston explained, “there’s a hole a meter across and quite deep. If you step into it, you disappear. A few seconds later you pop back up, wash over the edge, hit the rock below and get smashed around a bit against the wall until eventually your remains get spat out.” Like a manhole, the danger is forgetting it’s there, he said, “so just remember it’s there.”

We carried our inner tubes over our shoulders when traversing shallow stretches and wore them around our middles when jumping off the waterfall; the rest of the time, we sat in them. We were advised to keep our hands and feet close to our tubes: Besides the danger of hypothermia--the water is cold--the only potential injuries seemed to be occasional minor scrapes and bruises from the cave walls.

Psychological dangers are another matter entirely.

There’s the whole range of claustrophobics, for instance. Johnston said he semi-regularly escorts people back to the parking lot who “hadn’t realized they even had a problem.” Sometimes a participant will confess a “small” problem with claustrophobia only to faint dead away at the entrance to the cave; then again, many claustrophobes go through the caves specifically to conquer their fears, and usually succeed.

Those who have problems with things that go slither in the dark may be uncomfortable to learn that cave denizens include eels, and giant locust-like insects called wetas. But any stories about wetas attacking headlamps and attaching themselves to cavers’ faces are entirely untrue, Johnston said.

For no discernible reason other than the fact that I may have asked more questions than the others, our guide appointed yours truly “leader.” I was giddy with excitement: While everybody else could follow the headlamp of the person in front of them, there was nothing in front of the leader who, in this case, had no idea where he was going.

We began walking through water that varied from ankle- to knee-deep, but soon it was deep enough that we sat in our inner tubes and let the current carry us along. The guide brought up the rear.

The cave walls fascinated with their striped and mottled patterns. At times, the ceiling was so low that we had to get absolutely flat to our tubes to proceed. Stalagmites and stalactites were seemingly unfinished, roughhewn rather than refined. Whenever we proceeded without headlamps, it was surprising how sensitive our natural radar was, how accurately we could sense the distance of the walls.

There are two routes over the waterfall, the lower and more popular involving a short drop that the whole family can manage. The other jump starts some 12 feet higher, with an approach that requires climbing a ledge halfway up the cave wall, then traversing along one side of the cave to a somewhat intimidating jumping-off point. (As it turned out, the men on our trip took the high road, the women the low.)

We took the plunge one by one. Jumping styles ran a gamut from gingerly to prudent to cannonball, and some took more water up the nose than others. But all of us followed Johnston’s admonition about getting a “death grip.”

If the waterfall jump was the expedition’s high point from an adventure aspect, the aesthetic high point followed soon after. A shout of “Eel, eel!” indicated not that we should panic because something was about to bite us, but rather that we organize ourselves into a conga-like formation by clutching the legs of the rafter in front of us and turning off our headlamps.

The “eel” thus formed kept us together in the dark while allowing for maximum enjoyment of our middle-earth observatory--of those nether stars with their otherworldly white-green light, some near and others seemingly light years away at the top of enormously high caverns.

The glowworms responsible for this enthralling display are more precisely described as the larvae of the funga gnat, or glow-maggots. They remain in their cocoon state--the hungrier, the more radiant--for about a year before hatching; they then mate nonstop for three days before ultimately, and not surprisingly, expiring.

The nature of our wonder changed when we passed beneath a more genuine window to the heavens, a shaft of at least 200 feet showing daylight at the top. And finally we also saw light at the end of a tunnel that was, for once, more literal than proverbial. Interestingly, every one of us began hand-paddling more quickly.

After exiting the cave, we had the choice of rafting back along the tributary to the parking lot or walking back; all of us chose rafting. The shift from dark to light also revealed an inner catharsis, as if we’d together exited some enormous womb: Strangers when we entered the cave, we now raced each other back with childlike exuberance, splashing, having mud fights and generally celebrating the joy of sunshine regained.

GUIDEBOOK

Washing Along in Waitomo

Getting there: Hertz, Avis and Budget rental cars are available at both Auckland International and Rotorua airports. To the caves, take State Highway 1 south from Auckland to Hamilton, continue south on State Highway 3 to Hanatiki, then turn off to Waitomo. Auckland to Waitomo is 125 miles; Rotorua-Waitomo, 95 miles.

When to go: The Caves are open year-round. I went during the New Zealand summer (December-February), when the coolness of the caves could conceivably provide a respite from the warm weather above.

Rafting tours: Tours depart daily on the hour; allow three hours. Cost for the tour is roughly $25, and includes wet suit, helmets and headlamps, hot showers and a snack. Booking ahead is essential; in New Zealand, contact the Museum of Caves at (0813) 87-640. (Minimum age is 12 unless prior arrangements are made.)

For more information: Contact the New Zealand Tourism Board, 501 Santa Monica Blvd., Suite 300, Santa Monica 90401, (800) 388-5494.