The tourists appear to be blocking one lane of the coastal road outside Tárcoles, a busy thoroughfare that sees a lot of serious 18-wheelers coming and going from the Pacific port of Caldera. When the first burly local driver arrives with his rig and brakes, he appears a bit distressed. He looks thoughtfully at the bus and at the foreigners lined up along the highway. None of them, however, look at him. Their binoculars and cameras are fixed on the astonishing sight of six scarlet macaws in a nearby ceiba tree. Scarlet macaws in the wild are mind-bending, the total technicolor parrots, flaunting every color in the rainbow. To realize that we still share the ordinary world with the scarlet macaw, that it's not some kind of copyrighted entertainment phenomenon in Orlando, Fla., is to hope good things for the future.

The truck driver puffs out his cheeks and shakes his head. The entranced bird-watchers, ogling and filming away, never glance away from the treetops. The driver carefully drives past the 20-passenger Toyota tourist bus. He isn't happy, but he doesn't take it out on the turistas.

Travelers in this hemisphere will know that this can only be Costa Rica, a land of great beauty with a commitment to democracy and reasonableness that has guided its history and its public life for 50 years and longer. This is not to say that, in Costa Rica, some hothead may not flatten you for bending his fender rounding some pothole on the Interamericana, or that ill will does not exist. But Costa Rica is a land of good intentions.

In Costa Rican society, the frictions of daily life are eased by humor and politeness. Relatively unused to foreigners before their ecotourist boom began in the 1990's, the egalitarian ticos still take visitors one on one, so to speak.

In its history, Costa Rica shares much with its neighbors up the isthmus. It has at times been as impoverished as they, reduced to the mercy of foreign fruteros. With the spread of coffee cultivation in the mid-19th century, an overheated prosperity based on monoculture brought wealth to a handful of families whose descendants have traditionally served as a ruling class. It is the differences, however, that have distinguished Costa Rica in the region.

By now, Costa Rican exceptionalism is a near cliché, but it is based on some facts of life that one doesn't have to be a sociologist to recognize. This is the only country in Central America that abolished its army as a constitutional reform -- its fortified barracks overlooking San José are now the National Museum. It takes deep pride in a welfare state that labors to retain a nationwide social safety net in a country not unscathed by recent economic developments.

Amazingly, this very small country, half the size of Kentucky, contains the greatest variety of plant species on earth as determined by the World Resources Institute, along with 615 separate species of bird and mammal. This abundance exceeds that of any country in Africa and proportionally rivals Brazil's.

A few things seem worth saying about travel to this spectacularly beautiful place. One is that the national park system is the repository of its national treasure and that the best places to stay adjoin parks and adjoin them as inconspicuously and harmoniously as possible. The other, to the many people who normally do not consider traveling in groups with guides, is that easy access to national parks in Costa Rica is best afforded that way. Animals in the forest make a point of being hard to see. Guides are trained to see them and, unless one is a skilled spotter or bird-watcher, extremely helpful.

My wife, Janice, and I were part of a group of 11 Americans, all well traveled, touring under the auspices of Overseas Adventure Travel of Cambridge, Mass. Our 13-day itinerary took us generally north and west of the capital, San José, once descending to the edge of the Caribbean slope as far as the Sarapiquí River area and its Centro Neotrópico.

The centro is an eco-tourism complex established by presidential decree in 1997 at the entrance to the Tirimbina Rainforest Preserve. It's a trip of a few hours from the capital over paved roads, almost 50 miles from the Caribbean itself but with the terrain that exemplifies the jungles on the east side of the Central American Great Divide.

At Sarapiquí there are gardens and one of the country's few anthropological sites. Maleko Indians left 70 burial sites here, along with some pottery and petroglyphs. There's a small, well-appointed anthropological museum near the site and a pleasant bar to reflect on it all while listening to howler monkeys and catching the rain-forest breezes. We were traveling in the late-summer rainy season, but our first few days were spared spectacular downpours.

The centro offers accommodation in large rooms within thatched buildings in the pre-Columbian village style. The Tirimbina preserve, 820 acres of rich tropical woodlands, is easily accessible across suspension bridges from the Sarapiquí complex. Trails lead through Tirimbina, and, for visitors who want a closer experience of the Sarapiquí River, guided white-water rafting. The rapids are fun, novice class, and along the river, creatures abound: iguanas, sloths and basilisks, along with enough exotic birds to provide regular new entries in a birder's logbook.

Our next destination was in the humid tropical forest of the Bosque de Chachagua, not far from the volcano at Arenal. We spent an hour in the town of Quesada, buying meat and vegetables to be cooked later at our hotel, a cluster of pleasant but basic cabins on a hillside. Maintaining the good will of a market stall merchant while attempting to purchase a food item you most imperfectly pronounce -- which in fact you have never tasted, which could be for all you know animal, vegetable or mineral, which in fact you would not recognize if a three-toed sloth hit you on the head with it -- is a reasonable test of a town's civility. For the patience and kindliness of the market people of Quesada -- may they long prosper in happiness.

From the hotel we made some novel expeditions -- novel at least for me. One such took us to the San Rafael de Chachagua elementary school, where Elizabeth, aged 11, made me dance the Zapateada, waving my checkered bandanna while she twirled prettily before me. Nor was I released until I had seen the sixth grade's garden, met its pets, listened to Elizabeth read ''Mr. Gilligan's Pig'' in resolute inglés. The children seemed delighted to entertain foreign visitors, and our group of Americans, mostly teachers, responded enthusiastically.

For lunch several of our band visited the home of one of the students. By this time we had discovered that food in Costa Rica is noticeably good, and the home-cooked meal (rice and beans, beef, hearts of palm, with coconut rice pudding for dessert) was even better. After lunch we spent part of the afternoon playing dominoes, in a fractured mixture of Spanish and English. If anyone had suggested a year before that I would spend a September afternoon playing dominoes in San Rafael de Chachagua -- I would have been, well, puzzled.

Also from Chachagua we traveled north to the great Caño Negro swamp, a vast expanse of wetlands that are known in Costa Rica as llanuras and are reminiscent of the Everglades. Much of this area is national park or wildlife reserve; it's scarcely inhabited and, being close against the Nicaraguan border, was further depopulated by the contra wars of the 1980's. The town of Los Chiles is a river port on the Río Frio with a back-of-beyond feeling. Here boats arrive from Nicaragua with Nicaraguans applying for Costa Rican labor permits. (Several dozen were turned away by the border police the day we turned up.) At Los Chiles one can rent a boat, with a guide, to go farther into the area along the river. The shores are a mixture of private and public land; there are Brahman bulls placidly feeding in the Caño Negro, which happens to be one of the top spots in the country for reported jaguar and puma sightings. The river and its shores are teeming with life. The principal amphibian here is the innocently Pogo-esque caiman, which, sometimes achieving a snout-to-tail length of five feet, is too big to be funny. Birds migratory and specific are seen in great numbers; there are parrots and huge Amazonian kingfishers, hot blue and iridescent green mangrove swallows, white ibises and roseate spoonbills, wood storks -- a list would be pages long.

All four types of Costa Rican monkeys turn up here, the white-faced, the spider, the squirrel monkey and the ubiquitous howlers whose alpha males will soon be driven unhinged by mimicking tourists challenging their supremacy over the band. The Caño Negro is a dreamscape that leaves an imprint on the imagination: its waving grasses, punctuated by ceibas and the enormous conspiring sky, suggest infinity.

For a gently inclined, highly civilized country, Costa Rica yielded a disproportionate number of spectacular experiences, perhaps the most impressive of which was the eruption of Monte Arenal, one of the nine active volcanoes in the country. We arrived in the town of Fortuna to see the mountain that loomed in the range above us on the front page of the paper La Nación. The night before, it had blown, spewing golden lava far down its northwestern slope, which was fortunately where it was expected, having been smoking and tossing molten rock down since 1968. The 5,357-foot Mount Arenal destroyed two villages and killed about 80 people during the 1968 eruption, and it continues to take a toll of the occasional rash tourist and guide who decide no visit there complete without going eye to Cyclopean eye with the great mountain. For two nights running, from the very comfortable, well-provisioned bar of the Volcano Lodge -- even from the terrace of our well-situated room -- we watched Arenal, when it was not covered with cloud, fume and glow with earth's fire, roaring like a fiend. The lodge, with air-conditioning, cable TV, pool and Jacuzzis from which to watch the volcano, was about the most upscale accommodation on our route.

The next day, we went over the Cordillera de Tilarán and Costa Rica's continental divide into the dry tropical forest of Guanacaste province, much of it actually open savannah that supports the culture of the sabanero. The classic sabanero is the tough mounted herdsman of these plains, known in the old cowboy way as independent, chivalrous and capable of iron endurance. Fancy saddles, good horses and skilled riding are admired and many towns in Guanacaste feature a rodeo, called a tope, where the main event is bull riding. We stayed at the Buena Vista Lodge and Adventure Center, an extensive former cattle ranch at the entrance to Rincón de la Vieja National Park, where accommodations in interconnected, motel-style buildings are basic but comfortable. Here in the drier forest the rainy season overtook us, but only intermittently.

Horses and thermal mud baths were available, but our favorite diversion was the canopy tour, an operation in which the tourist rides a wire on a kind of breeches buoy from elevated platform to elevated platform at a speed controlled by a hand brake, literally one's hand encased in a leather glove. High-minded and unexcitable persons are invited to inspect the scenery and the perspective on nature afforded by a view from the treetops. Most people, I think, succumb to the sheer kick of the thing, as we did, zooming through the branches at high speed. The monkeys we expected to hoot and jeer had apparently seen enough of human folly and failed to show themselves. But the landscape, from the high peaks of the Vieja volcano to the Pacific miles to the west, was breathtaking.

From the old port of Puntarenas, sleepy and louche in the rainy season, one may take a party boat across the Gulf of Nicoya to a point on the Nicoya Peninsula called Punta Coral, where a private reserve offers a beach with cabanas. Kayaks and snorkeling equipment were available, and an elderly gentleman, professionally know as Abuelo, played the marimba at lunch even for those whose beach toy was a hammock.

We finished near the Tárcoles River, staying again at the edge of a national park, in this case the Parque Nacional de Carara. The mangrove swamps of the world, it is now known, play an important role in the vitality of the world's oceans, and they give a home or shelter to an uncountable number of bird species.

And, quite close up on the Tárcoles River, we watched a 13-foot crocodile challenged on the riverbank by a man armed with nothing more than a green towel. The crocodile went for it, and the sound of those jaws snapping shut is still with us.

Photo: The caldera of the Poás Volcano, on the way to Sarapiquí; fauna around the Tárcoles River ranging from crocodiles to butterflies; the thrill-a-minute canopy tour at Rincón de la Vieja.; Scaling a coconut palm; painted ox carts are a Costa Rican tradition; iguanas in conversation; students at the San Rafael de Chachagua school.; Two places to relax / aboard a tour boat on the Tárcoles River, and the thermal springs at Buena Vista Lodge. (Photographs by Robert Lewis for The New York Times) Maps of Costa Rica