Baulas Marine National Park is one of the few places on earth to see leatherbacks

We were standing at the edge of the Pacific Ocean in northwestern Costa Rica, looking down a three-mile sweep of tropical beach along the Pacific shore. The sun was hot, the sand blinding bright, and the waves ideal for bobbing or body surfing. But perfect as it seemed, our family wasn't here for the beach. We had come to see leatherback turtles.

Playa Grande, the centerpiece of a six-mile stretch of Costa Rican seashore known as Baulas Marine National Park, is one of the few places on earth to see leatherbacks. The largest of the world's seven species of sea turtle, leatherbacks come ashore from late October to early March to lay their eggs in the sandy berm just above the high tide line. Our visit during the week surrounding New Year's was late enough in the nesting period that we expected to find baby turtles hatching as well as adults laying eggs.

Leatherbacks, like all other sea turtles, are suffering from human activity. The beaches where they nest are being developed, and they are drowning in fishing nets and choking on plastic debris (which they apparently confuse with jellyfish, the staple in their diet). In may areas of Central America, including Costa Rica, their eggs are collected by indigenous peoples to be eaten or sold. There are only a few dozen places in the world where leatherbacks lay their eggs, and only four beaches where they come in large numbers. Playa Grande is, along with beaches in western Mexico, the East Indies and Guyana, one of those favored spots.

Our charter flight from Detroit landed at the tiny Liberia International Airport in the northwest corner of Costa Rica. The sun was brilliant, the wind hot and dry, and the airport's waiting room nothing but an open air snack bar under a barn-like thatched roof. It took almost an hour to get through passport control. A man from our car rental company was waiting by the baggage claim and after we completed the necessary paperwork we were on our way.

Our hotel, Villa Baula, was at the southern end of Playa Grande, and hour's drive from the airport. The roads were esasy to follow, although we did stop to ask for directions in the town of Huacas. But once we got on the bumpy dirt road leading along the lightly developed shoreline we just followed a series of small yellow signs with a stylized outline of a "'Baula" - the Spanish word for leatherback turtle - to the hotel.

The Villa Baula is simple, compact and attractive. Surrounded by trees, it has a swimming pool and a open-air thatched-roofed restaurant that is separated from the beach by a narrow strip of thorny forest. Twenty of the hotel's 25 units are in twin two-story structures, but we had reserved one of the two-bedroom bungalows and were delighted with what we found.

Our wood-walled, tin-roofed cabin sat on stilts about eight feet above the sandy ground. The bedrooms had ceiling fans and large screened windows to let the evening breeze blow through. The porch, equipped with ceiling fan, picnic table and refrigerator, was ideal for reading, sitting, or watching iguanas and birds move about in the leafy forest. It was like the Swiss Family Robinson with electricity. Our neighbors, divided about equally between Costa Ricans and Americans, included a group of college students traveling with a biology professor.

That evening, on an exploratory walk along the ocean shore, we passed half a dozen places where sea turtles had crawled across the beach. Their trails - swaths of deeply tracked sand about four feet wide emerging from, and returning to, the shallow waters of the pacific - looked as if they had been made by some sort of otherworldly bulldozer. We followed one to the spot where a turtle had dug her nest, and could see how she had wandered in brief confusion (or perhaps in deliberately confusing circles) before heading back to the sea. The leatherbacks were here, and we would be able to see them.

Tired from the journey, our 15- and 13-year-old daughters, Ruth and Elaine, fell asleep soon after dinner. But my wife, Beth, and I didn't want to wait. At Playa Grande the leatherbacks come ashore at night, generally at high tide (which that night was at about 11). To protect the turtles, visitors are not allowed on the beach at night without a guide. At around 10, Beth and I walked to a park ranger's shelter a few dozen yards from the hotel. We hadn't signed up for a tour with Villa Baula, but there were four guided groups from nearby hotels going out that night and the ranger assigned us to one. We paid the guide $10 apiece ($6 was for park admission) and when a park employee with a walkie-talkie signaled that a turtle had come ashore, our group of about 20 headed down the dark beach.

A few yards down the shore we gathered around the guide for a quick review of turtle-watching etiquette. Light can confuse or frighten the turtles, so we were told not to use flashlights or take pictures using flashes (which effectively ruled out cameras, since it was dark). We were also warned to be quiet and to stay away from the turtle's head and out of her field of vision - and, of course, no touching.

It was all common sense, but it helped remind us that we were guests on the turtles' beach. We followed the guide's red-lensed flashlight to "our" turtle. Each group observes one animal, and if it happens to come ashore a long way down the beach the group may have to walk as much as half a mile. But our turtle, not more than 100 yards from the ranger's shelter where we were waiting, had already crawled up the beach and started digging a hole for her eggs. The group quietly gathered in a half-circle behind her.

We had read that a typical adult leather-back is four and a half to five a half feet long and can weigh more than 1,000 pounds, but we were still surprised by the turtle's sheer bulk. It was as big as an oil drum with wide flutes running up and down its body and long front flippers splayed out from the front of a dark, leathery-looking carapace. The back of the turtle's shell was sharply pointed, and in the dim red light of the guide's flashlight we could see her supple back feet scooping out a deep, narrow hole.

Nothing about the process happened quickly. A foot would stretch down into the hole, pause for a few breaths, then pull out a cup or two of sand. After another rest the foot would scoop again, then the turtle would change feet. When the hole was between two and three feet deep, she stopped, rested for several minutes, then began laying eggs.

We took turns watching the eggs drop, like rubbery oversize golf balls, into the hole. After 40 or 50 were laid, a dozen or so noticeably smaller eggs came out, and then the turtle stopped. She tamped down the eggs with her flipper, pushed some sand on top of them, and repeated the process until the hole was nearly full. Then she began flapping sand around with her long front flippers, making a slow, methodical "whap, whap, whap" that sounded like someone beating a carpet. In the end, the place where she had nested was hugely obvious - a churned-up circle of sand 8 to 10 feet in diameter - but the location of the actual nest was impossible to see. After watching this process for about a quarter of an hour, we were led back to the hotel by our guide. From start to finish, we had spent more than two hours on the beach.

The next morning, still sleepy, Beth and I were lagging behind our daughters as they ran down the shore, picking up shells and skittering like sandpipers across the wet sand. Then they turned away from the water toward the narrow stretch of low dunes at the back edge of the beach and began waving wildly. They had found six newly hatched leatherback turtles working their way toward the ocean.

The baby turtles were no more than three inches long, matte black and incredibly cute. Like little mechanical toys, they pulled themselves across the sand with their front flippers: flip, pause, flap, pause, again and again, advancing perhaps half an inch with each flip or flap, across 20 to 30 yards of beach. The urge to help was almost irresistible (and once we saw someone who couldn't resist) but we had heard that this struggle to the sea helped imprint the location of the beach in the baby turtle's brains, so we just stood and watched - even when waves tumbled the turtles 10 or 12 hard-won feet back toward the shore.

And eventually, as they have for millenniums, the tiny creatures reached the water and disappeared. For most of that week the leatherbacks were the focus of our lives. We went out three more nights to watch the nesting, twice staying long enough to see the mother crawl back down the shore and vanish, like a wave-washed stump, into the ocean. On two other mornings we saw baby turtles heading for the sea. We saw one get eaten by a vulture and watched out of the sand that covered their nest.

And one morning toward the end of the week, just after sunrise on a day when high tide was late at night, we saw an adult turtle finish her nesting in daylight, lumber back to the water, and swim with Olympian power and grace out to sea.

Although we devoted mornings and nights to the turtles, there was plenty of time during the day to enjoy other attractions. We lay in the sun and body-surfed in the warm waves. We wandered up and down the nearly deserted beach of ivory-colored sand, collecting shells and watching pelicans and frigate birds cruise along the line of breakers. We asked the hotel to arrange an afternoon boat tour of the Tamarindo Estuary Wildlife Refuge, a 1,500-acre maze of narrow waterway sand mangrove-tangled islands just behind the Playa Grande beach ($12 a person plus $6 admission to the park), and saw some small crocodiles, a family of howler monkeys, a variety of birds, including a ibis, a large, hawlike caracara, several kinds of heron, and a small kingfisher, and lots and lots of mangrove trees.

Another day we drove our rented sedan about four miles to a rocky headland at the northern end of the park, where, we snorkeled in sheltered tidal pools and watched tiny iridescent fish swim in their natural aquariums.

One evening we visited the small privately run Leatherback Turtle Museum, about two miles north of our hotel, which featured an informative photographic exhibition about the turtles ($5 for the 15- to 20- minute audio tape tour) and a gift shop stocked with turtle-themed souvenirs.

Still, most afternoons we were happy to lounge in the sun or sit on our cabin's shady porch, l watching iguanas nibble on fallen flower blossoms and exotic birds flutter through the foliage around us.

The food in the hotel restaurant - mostly pan-fried fish, chicken or beef, and gallo pinto, Costa Rica's tasty version of rice and beans - was perfectly acceptable and the staff couldn't have been more accommodating, but after three days we had run through the menu and began looking for other possibilities. Lunch (fried fish, hamburgers, and fruit drinks) in the airy dining room of a small hotel called Las Tortugas, a few mile up the beach, was slow but pleasant. We had a very good dinner at the Cantarana hotel just up the road from Vila Baula (broiled fish and pasta in a spicy tomato sauce, both perfectly cooked and attractively presented), where a dash of European formality contrasted nicely with the open-air setting. We even enjoyed a midday visit to the dusty, touristy town of Tamarindo, a surfing and beach resort half an hour's drive away, where we had sugary pastries from Johan's Bakery and some delicious passion fruit, pineapple and tamarind fruit drinks from a juice bar across the road.

These little expeditions were always pleasantly low-key and un-rushed, and more days than not we didn't venture beyond our quiet beach. We had adopted the pace and schedule of the sea turtles, and we found that it suited us perfectly.

JOHN R. ALDEN