13 Best Sights in Vieques and Culebra, Puerto Rico

The not-so-secret Secret Beach is a heavenly cove for those seeking privacy. This tiny yet beautiful horseshoe-shape stretch of sand, reached via a rambling dirt road, is calm and secluded. You can find yourself completely alone or in the company of just a few couples embracing in the crystal clear water. Amenities: none. Best for: solitude; snorkeling; swimming.

East of Esperanza, Puerto Mosquito is one of the world's best spots for a glow-in-the-dark experience with undersea dinoflagellates—microorganisms that light up when the water around them is agitated. Local operators offer kayak trips or excursions on nonpolluting boats to see the bay's light show. Look behind your boat at the twinkling wake. Even the fish that swim through and jump from the water bear an eerie glow. The high concentration of dinoflagellates sets the bay apart from other spots (including in Puerto Rico) that are home to these microorganisms. The experience is best when there's little or no moonlight; rainy nights are beautiful, too, because drops hitting the water produce ricochets that shimmer like diamonds. Note that licensed operators are prohibited from leading tours on the day before, during, and after a full moon.

Just east of Esperanza, this mile-long stretch of sand skirts a perfect crescent-shape bay. Dotted with picnic tables, this beach gets packed on holidays and weekends. On weekdays, when crowds are thin, you might see wild horses grazing among the palm trees. There is a small fee for parking, but often there is no one at the gate to take your money. Amenities: food and drink; parking (fee); showers; toilets. Best for: snorkeling; swimming; walking.

This Spanish-built lighthouse above the ferry dock in Isabel Segunda dates from 1895. It was built to guide vessels into the harbor, which is surrounded by a chain of dangerous reefs. Its red light is rumored to be visible from as far away as St. Croix and St. Thomas. In 1992, the elegant structure was carefully restored and transformed into a maritime museum that traces much of the island's history, including the visit by South American liberation leader Simón Bolívar. The tiny museum is open weekdays, but the lighthouse itself is worth a look any day.

On the island's northern coast, above Isabel Segunda, is the last military structure built by the Spanish in the New World. It was erected in 1840 at the order of Count Mirasol, then governor of Puerto Rico. Although it's tiny, it took more than a decade to complete, which meant Mirasol had to repeatedly ask for more money. (Queen Isabel, on being petitioned yet again, asked Mirasol whether the walls were made of gold.) The hilltop fort helped solidify Spanish control of the area, keeping British, French, Dutch, and Danish colonists away and dissuading pirates from attacking Isabel Segunda. In 1991, after sitting empty for several decades, it was transformed into a museum with a good array of artifacts from the Taíno and other cultures that thrived on this and nearby islands before the arrival of the Spanish. It also has an impressive collection of small arms, plus exhibits on the island's years as a sugar plantation and its occupation by the U.S. Navy. On occasion, it presents temporary exhibitions of works by contemporary artists.

In the evening, there's no better way to enjoy the sunset than a stroll along Esperanza's 200-yard-long Malecón, a waterfront walkway running the length of the beach.

One of the first stretches of sand east of Esperanza, this well-maintained beach boasts covered cabañas for lounging. Less rustic than other nearby beaches, it is sheltered from waves. Amenities: parking (no fee); toilets. Best for: snorkeling; swimming; walking.

People staying in any of the inexpensive accommodations in Esperanza can simply walk across the road to this beach. There's good snorkeling across the bay around Cayo Afuera, an uninhabited islet, and by the derelict pier. Manatees are occasionally spotted here, as well as barracudas and nurse sharks. If you're looking for swimming or sunbathing, keep moving; there are much better beaches nearby. Amenities: none. Best for: snorkeling; walking.

Some consider this the most beautiful beach on Vieques. It has a handful of covered cabañas with individual parking spots, so guests can claim their own personal stretch of sand and survey an expansive, tranquil horizon. Beware of strong surf in some spots. Amenities: none. Best for: solitude; walking.

Ideal for families because the water is calm and shallow, this is also a good spot to try snorkeling. There are no facilities. Amenities: none. Best for: families; snorkeling; swimming.

On the western edge of the island, at the end of a long unpaved road marred by potholes, this beach faces the Vieques Passage. Miles of coral reef just offshore attract snorkelers and divers, but caution is required due to strong currents. From the shore you can catch a glimpse of El Yunque on the mainland. Amenities: none. Best for: snorkeling; solitude.

The Vieques Conservation & Historical Trust was established to help save Puerto Mosquito, one of the last remaining bioluminescent bays in the world. The small museum, located on the main drag in Esperanza, has interesting information about the bay, as well as the island's flora and fauna and history. A little pool lets kids get acquainted with starfish, sea urchins, and other denizens of the not-so-deep. There's also a tiny gift shop, the profits from which are funneled back into the foundation. Call ahead if you're coming at lunchtime, as the place is sometimes closed for an hour or more. If you're interested in history and architecture, ask about a guided tour of the Playa Grande sugar mill ruins.

A portion of the west and the entire eastern end of the island is administered by the U.S. Fish and Wildlife Service as the Vieques National Wildlife Refuge. With almost 18,000 acres, it's Puerto Rico's biggest protected natural reserve; in 2015, it was voted the fourth-best refuge in the entire Fish and Wildlife system. Many of the beaches on the northern and southern coasts—where an asphalt road leads to six of them—are open to the public. Hiking, biking, and horseback riding are allowed on designated trails. Fishing (both shore and from kayak), swimming, snorkeling, and diving are also permitted in designated zones. Much, though not all, of the eastern region is pristine, astonishingly beautiful, and well forested, with a hilly center region overlooking powder-white sandy beaches and a coral-ringed coastline. Some of the refuge—including 900 acres that once served as a naval bombing range—remains off-limits to visitors, though, as authorities continue to search for unexploded munitions and contaminants, the byproducts of the area's 60 years as a military base.