I imaged the Galapagos to be a pile of rocks in the middle of the ocean where prehistoric creatures walked around--turtles as big as Volkswagens, lethargic lizards and birds with blue feet doing mating dances in a National Geographic TV special. It is one of those places that you vow to see once in your life, like the Grand Canyon and the Eiffel Tower.

Expecting a tranquil zoo without cages, I found instead a stark and sometimes fearsome landscape as magnetic as the animals I came to see. The Galapagos Islands, 600 miles off the coast of Ecuador, are primarily shallow lumps of lava with no fresh water, little soil and few plants, save cactuses and bare trees tolerant of saltwater and equatorial heat.

Charles Darwin found the place inhospitable, saying, "Nothing could be less inviting than the first appearance (of the Galapagos)."

Nevertheless, the moment he landed here in 1835 on a mapping expedition, he was hooked. Sailing a mere five weeks in the islands, he discovered a living laboratory of fantastic animals and birds suspended in time, and from these he developed a theory of biological evolution.

On my way to a week's island cruise on the Albatros, an 80-foot dive yacht, I queued up in the airport in Quito. Khaki-clad travelers in hiking boots and floppy-brimmed hats inched toward the ticket counters with mountains of camera cases, tripods, dive bags, and backpacks. We flew to the island of San Cristobal, a simmering bit of earth precisely astride the equator, and within an hour, eleven passengers and I, and nine Ecuadorian crewmen of the Albatros, were anchored in a quiet bay fifty yards offshore of a rocky strip called Isla Lobos.

The divers roared off in a Zodiac with the dive master to be "checked out." I put on a bathing suit and snorkeling gear and jumped off the back of the boat into about twenty feet of clear, warm water. A hubbub of dark shapes flashed around me--a party of sea lions ignored my frantic thrashes and nosed my fins. Scary flutterings in the white sand below turned out to be a school of mustard-colored rays.

Later, with our naturalist guide Mathias Espinoza, we took a sunset stroll on the islet. Beside the trail were lava lizards, red-headed yellow warblers, Darwin finches, and Sally Lightfoot crabs in fluorescent red, orange and blue, brilliant against the black lava rocks. An encampment of a dozen or so blue-footed boobies peered calmly at us as we took photos in the fading light. Acrobatic frigate birds and a leaping gaggle of sea lions chased our Zodiacs back to the boat. The surprise of this day was that we encountered so many creatures, so soon, and they didn't seem to mind.

Cruising all night in a rollercoaster, September sea, we reached the island of Espanola in the early morning under overcast skies. We scrambled off the Zodiacs in a "wet landing" that had us clutching our cameras. Our bright jackets were the only colors in a bleak field of gray and black lava washed with snowy guano. Faint honking and clicking sounds drew us along the trail into a swirling mist.

Espanola's rocky fields are the nesting site for virtually all of the world's waved albatrosses, about 12,000 pairs (except for a few pairs that nest on tiny Isla de la Plata near the coast of Ecuador). With seven-foot wingspans that take them far out to sea for literally months at a time, the birds have bulky, streamlined dark bodies and graceful, ivory-colored necks and heads with powerful, long yellow bills. Of all the birds we saw in the islands, the waved albatrosses were the shyest. At the sight of us, they lumbered up off their nests like 747s, leaving eggs and fuzzy chicks below.

Unruffled by tourism, the blue-footed boobies determinedly crammed small fish down the throats of their young as we walked near their nests, each shaded by chalky salt bush branches. The boobies whistle and click, waddle, rock from side to side, bow, tip their heads back and stretch their pure white necks to the sky like slow-moving clowns. Their big, beautiful, webbed feet are neon-bright, light blue or turquoise, baby blue, gray-blue, sky-blue, every blue imaginable.

In a half-day of wandering on the island, our sightings included legions of fat red and black marine iguanas. Subspecies endemic to the island, the black, yellow and green Espanola lava lizard and the Espanola mockingbird exist only on the twenty-four-square-mile remnant of a volcano. An aggressive mockingbird made his presence known by pecking at our daypacks and hopping around our feet, even sitting on our heads.

The Galapagos Islands, a scattering of nineteen small islands and scores of islets, were formed five to ten million years ago by underwater volcanoes erupting above the surface of the ocean. At the junction of two continental playes over a stationary "hot spot" in the earth's core, several of the volcanoes are still active. Eruptions have occurred as recently as 1991.

Great rivers of lava rolled across the island of Santiago just a century ago, melting into Sullivan Bay where buccaneers in masted ships watched in terror as the sea boiled and the sky burned. The vast, cracked lava sheets host little obvious wildlife except a few sea lions, crabs and penguins at the water's edge. An occasional fist of cactus sticks up, and wispy, orange mollugo plants cling here and there. We hiked into the silent inner island under a relentless yellow sky. Black and rust cinder cones and the tongues of new land seemed as young as the day the island was born. Walking gingerly across a ropy, silvery-black surface dodging bubbles and fissures that looked as if steam might hiss out, I could almost feel the heat melting the soles of my boots and could hardly wait for the promised afternoon of snorkeling in the coral gardens off Isla Bartolome.

More than half of the National Park of the Galapagos is under water. Tourists who dive or snorkel have double the wildlife sightings and a very different experience than on the arid islands. At the confluence of both equatorial and coastal oceanic currents, the seas here are actually rivers of widely differing temperatures, ranging from about 55 to 85 degrees, resulting in a marine environment inhabited by a high proportion of endemic species. December through June brings warm currents from Panama, when the weather is very hot and very wet. July through November is called the "mist season", when cooler currents from the south make for heavier seas and lower visibility, although diving is good every month of the year.

Snorkeling around a coral tower a few yards from Bartolome beach, I swam through schools of yellow and black surgeonfish, electric-blue parrot fish and angelfish. Sea lions were everywhere, almost elbowing me out of the way in their enthusiasm. Having snorkeled with the lions for a few days, I no longer panicked when one of the sleek fellows bared his teeth and stared into my mask.

Floating peacefully, watching a gang of sea horses propel themselves delicately along, I looked up to see a gray wall, then white flashes, then an eye. White-tipped reef sharks may be harmless in these waters, but this was my first shark. I swam backwards at high speed and scrambled out of the water onto a rock. Starting to breathe again, I realized that two penguins, each about eighteen inches tall, were standing beside me in their "tuxedos". They turned their black backs and faced the black lava, believing themselves to be invisible.

Returning to the safe cocoon of the Albatros, we snorkelers were greeted by Walter, the barman, in his black tie and starched white shirt, with a tray of hot hors d'oeuvres.

That evening, after I recounted my little shark encounter, Mathias told us stories of some of his 3,000 dives in the Galapagos. He said it is common to see huge schools of hammerhead sharks, bottle-nose dolphins and manta rays twenty feet across.

Until a few years ago, tourists often fed reef fish and rays, stroked the sea lions and even sat on the big land tortoises. Now, with annual visitors topping 50,000 a year, licensed guides police their tour groups, educating them about the cumulative effects of touching, feeding and even taking flash photos and smoking. Trails are clearly marked and are frequently moved to avoid habitat destruction and interruption of breeding and nesting.

A relaxing respite from days of hiking, snorkeling and diving was a late afternoon Zodiac ride into Black Turtle Cove, a maze of narrow channels bordered by mangrove thickets, a watery nursery for newborns away from the hungry predators of the open sea and a honeymoon resort for marine turtles. Shushed into silence by Mathias, who cut the outboard motor, we paddled on a green mirror beneath overhanging branches. Weak shafts of sunlight lit the sandy floor of the swamp and we looked down to see a mass of golden mustard rays, each about a foot across. A school of tiny gray sharks glided by, then rivulets of spotted eagle rays. A mating turtle couple locked in embrace rolled over and over at the surface of the water. About three feet long, these marine turtles are smaller by half than the most famous denizens of the Galapagos, the giant tortoises who live in moist, green highlands on Santa Cruz and a few other islands.

On the last day of the cruise, we anchored off Santa Cruz in the harbor of Puerto Ayora, the main town in the islands, and boarded taxis. The red dirt road to the tortoise preserve winds through the small town of T-shirt shops, open-air cafes and whitewashed block homes drenched in brilliant magenta waves of bougainvillea and hibiscus. Banana, guava and papaya trees stand in every yard.

At an elevation of about 1,800 feet in a fern-bordered, knee-deep grassy meadow, we found the tortoises. At the frist sight of one of the huge gray boulders, we all crowded around it, only to be warned off to a reasonable distance by Mathias. With a great whooshing sound, the boulder dropped, pulling his or her head and feet inside. A few yards away, another boulder moved, then another. Five hundred pounds of tortoise move slowly and they do eventually re-emerge to have their photos taken.

The 3,000 tortoises on Santa Cruz are a subspecies existing only on this island. Three of the fourteen subspecies of Galapagos tortoises, once numbering hundreds of thousands, are extinct. The remaining total population of 15,000 is gradually increasing due to the reintroduction of animals raised at the Charles Darwin Research Station in Puerto Arroyo. Some of the larger tortoises were born in the 1800s when whalers dragged the huge animals down to the ships to store alive for months of fresh meat. Now, they are simply gawked at by tourists and serenaded by flocks of vermilion flycatchers and yellow warblers.

On our last evening onboard, a band of musicians came aboard with guitars and banjos, and along with the crew, crowded into the lounge with us and we sang into the night.