If there's one word that describes Culebra--one of the last unspoiled islands in the Caribbean -- it's tranquility. Probably no other island goes to sleep or awakens so quietly. There are none of the sounds of bustling traffic, street sellers yelling their wares or tour guides imploring you to take their tours. Instead, you hear the occasional crow of a rooster, or, in the dark, a night heron's call. Otherwise, there is only the gentle lap of water against the piers or the trade winds sighing in the mimosa trees.

Seven miles long, three miles wide and shaped like a wishbone, sunny Culebra is 20 miles east of Puerto Rico's main island and 17 miles west of St. Thomas in the U.S. Virgins. It takes some effort to get to Culebra, but once there, yours may be the only footprints in the sands on any one of the island's peaceful, white beaches.

Most of Culebra's almost 2,000 residents live in pastel-colored houses clustered around the sheltered harbor in Dewey, the island's only town. Locally called Puebla, the fishing village was named after Adm. George Dewey of Spanish-American War fame. For years, Culebra was used by the U.S. Navy as a gunnery range and practice bombing site. In 1975, the Navy moved its firing range to Vieques, a Puerto Rican island southwest of Culebra.

Today, only a few reminders of the Navy's presence remain on Culebra: the island's few concrete roads and bridges, old Sherman tanks rusting in the undergrowth of Flamenco Beach and a microwave station still in operation on Flamenco Point. (Soon, however, this Navy connection will be gone also.)

The people who live on Culebra are friendly unflappable. Their pace is easy, and some stores don't keep regular hours. Shops close for lunch one day, but stay open the next. One store owner laughed when I asked why all the stores seemed to open different times. "Nobody's in a hurry to do anything here," she said. "Take it easy."

The "take it easy" attitude is one of the reasons for Culebra's tranquility. Another is that it has no specialty stores or shopping malls, so it's not an attraction for cruise ships. In Dewey, small, dusty grocery stores carry a little bit of everything, including delicious, finely ground Puerto Rican coffee and the seasoning known as adobo. A "mini-mas" sells everything from sundries to beach and kitchen equipment to shower curtains and writing paper. Two shops rent diving and snorkeling equipment and will arrange for a guide to take you to the reefs.

Most of Dewey's narrow, winding streets aren't named, but while you're walking on one of them in the early morning, your nose will lead you to the local bake shop. It opens at 6:30 a.m., and the proprietor sells long loaves of freshly baked white bread for 75 cents. Sweeter round loves filled with raisins also are a bargain. Have your morning coffee at the counter.

Culebra has abundant sunshine all year, with a mean temperature of about 80 degrees during the day. Nights are in the 70s and below. The easterly tradewinds, which blow most of the day, sometimes fool visitors into thinking the sun is not too hot, but it can burn quickly.

The island's dry period is from January to March. Heaviest rains are usually recorded from August to November; but rainfall averages only about 25 to 30 inches per year, so there are no gardens to speak of on Culebra. The ground is just too arid, and the desalinization plant sometimes doesn't produce enough water even for ordinary use. (When necessary, additional water is brought in on a large barge from Puerto Rico.) Even so, almost every yard boasts a banana plant or two, and papayas and coconut palms abound in some of the beach areas. Brilliantly blooming flamboyant trees; multihued, tissue-paper bougainvillea and flaming red hibiscus thrive in the hot, dry climate.

Away from town, the scrubby hills are criss-crossed with fincas -- small cattle ranches -- with holding pens and semiarid pastures, similar to the small ranches that dot Southern Arizona.

Residents and visitors alike seem to enjoy the remoteness of Culebra. One young couple and their 6-year-old son from Connecticut had the time of their lives bouncing around the island in a rented jeep. In spite of a number of problems -- a motorboat engine that died, making it a long row back to the shore, and a jeep without a gas gauge that (naturally) ran out of gas -- they found this unspoiled vacation spot delightful.

Jane, who works in the dive shop (no regular hours) near the ferry slip (open when the ferry comes in) and helps run the Coral Island Guest House, came to Culebra from New York City. "I love it here," she said. "I'm like lots of people who come here -- interested in nature. There's no night life, but who needs it? There are plenty of other things to do."

You can take your choice of nine uncluttered beaches. Some of the wilder ones on the Atlantic side require a trek down a rocky hillside. But others can be reached by walking or riding in publico -- the local taxibus -- over bumpy roads.

Beautiful Flamenco Beach is one of the best. There you can laze on the white sand, float in the gentle swells or swim out to explore one of the many coral reefs. On Flamenco Beach you'll discover a sense of timelessness, where the pressures of life all but disappear.

Or you can rent a boat and discover Culebra's sheltered coves or visit Isla Culebrita or Cayo de Luis Pena, two of the offshore islands that are part of the Culebra National Wildlife Refuge. Isla Culebrita -- with its hilltop lighthouse and crescent beaches -- and Cayo de Luis Pena are open from sunrise to sunset and visitors may debark. Permission to visit the other refuge areas -- 21 offshore islands and two tracts of land on Culebra -- must be obtained from the U.S. ranger at Lower Camp on Culebra. Some of the refuge islands are bird sanctuaries where white-tailed and red-billed tropical birds, boobies, sooty terns and frigates nest and rear their young.

Or you can go on a diving or snorkeling tour at prices ranging from $15 to $55 per person, depending on the number of dives. The price includes equipment, boat and guide. Culebra's surrounding coral reefs, especially the mile-long reef off Isla Culebrita, are outstanding for both snorkeling and diving, and you should go equipped with an underwater color chart so that you can identify the fish and coral.

Another outstanding side trip is a day sail ($30 per person with lunch) on the Katrina, a 45-foot sloop operated by Bruce and Kathy Goble. You sail out of Culebra's harbor, anchor in a quiet cove and take the tiny dingy to the reef. There you can snorkel in the clear aquamarine water or dive for conch. Then it's back to the sailboat for a delightfully fresh lunch and a rest. Later, you'll be ready for a swim or more snorkeling, perhaps along the mangroves surrounding Paco's Island, another of the little cays dotting Culebra's nearby waters.

Perhaps while you're resting after lunch or being lazy after your second swim, Bruce will tell you about some of the people who live on Culebra. High on a promontory, for example, stands an enormous house in isolated splendor. Moose and Abby, an older couple who retired to Culebra, have been building the house since 1973. One of the rooms was built especially to house a massive dining table 8 feet wide. Now Moose is building a campanile on the grounds to house the bells friends send him. Moose and Abby remain almost as isolated as their house, which is just the way they like it. As Abby said, "There's only the Atlantic between us and Europe."

And there are other, quite unexpected things to do on Culebra. When you've had your fill of snorkeling, you've sailed on Katrina, you've spent hours swimming in the gentle surf and lying on the clean, white sand, but still have the urge to do something else, you can help with the Endangered Caribbean Turtle Project. Culebra is the site of a special study of the nesting habits of the great leatherback turtles. And they are great: 6 feet from head to tail and weighing more than 800 pounds.

The study is under the direction of the U.S. Fish and Wildlife Service in cooperation with the University of Puerto Rico, the Conservation Authority of Puerto Rico and the National Marine Fisheries Service. Every night from early March through late August, Kathy Hall and Anton Tucker, marine biology graduate students, patrol Brava and Resaca beaches, observing the nesting habits of the leatherbacks and protecting their eggs. They are assisted by volunteers, and the project is partially funded by Earthwatch.

Literally working in the dark most of the night (no hotels light up these beaches), the Earthwatchers walk along the surf, watching for the turtles to emerge from the sea. After a turtle makes her way up the beach and begins to dig her two-foot-deep nest, flashlights are turned on so that data can be recorded. Earthwatchers measure the turtle, tag her flippers, count the tennis-ball-sized eggs as they are laid and mark the nests.

The Earthwatch volunteers help Kathy and Tony patrol the beaches every night, but visitors are a welcome addition to the crews. It's an experience your friends won't be able to top when you compare notes on your Caribbean vacations.

Unfortunately, it seems inevitable that change eventually will come to Culebra. It will be slow, however, so long as the wildlife refuges are protected and the local government turns deaf ears to developers. Culebra still is for those who are interested in nature.