500 Places to Take Your Kids Before They Grow Up highlights one-of-a-kind attractions around the world that are perfect to plan a family vacation around. The picks below offer a selection of swimming and snorkeling escapes in the U.S. and the Caribbean that are suitable for the young and old alike.

What: Swimming with a Million Tiny Lights
Who: Ages 4 & up
Where: Vieques, Puerto Rico

I thought Puerto Rico was an island -- but how can an island have an island? Well, Puerto Rico has two, Vieques and Culebra, for years well-kept secrets among Puerto Ricans, who come here to escape the tourists on the big island. Since the U.S. Navy in 2003 closed its installation on Vieques, though, much more land is available for vacationers, and Vieques is rapidly becoming known as an eco-friendly -- and still charmingly scruffy -- destination.

With some 40 palm-lined white-sand beaches, and reefs of snorkel-worthy antler coral off shore, Vieques -- 11km (6¾ miles) off the big island's east coast, only an hour by ferry -- has an obvious appeal for sun-loving families. But one of the coolest things on Vieques has nothing at all to do with the sun. Just west of the main town, Isabel Segunda, lies Mosquito Bay, which has been renamed Phosphorescent Bay for the way its waters glow in the dark, thanks to millions of tiny bioluminescent organisms called pyrodiniums (translation from science-speak: "whirling fire"). They're only about one-five-hundredth of an inch in size, but when these tiny swimming creatures are disturbed (by, for example, a hovering tour boat), they dart away and light up like fireflies, leaving eerie blue-white trails of phosphorescence. These pyrodiniums exist elsewhere, but not in such amazing concentrations: A gallon of water in Mosquito Bay may contain upward of three-quarters of a million such creatures. It's definitely worth letting the kids stay up late for once. Wear a bathing suit because it's possible to swim in these glowing waters, a sensation the kids will find incredibly eerie and cool.

Don't make the mistake of coming here on a full moon, however -- the glow of the pyrodiniums is only discernible on a cloudy, moonless night. (Warning: Some tour boats go out to the bay regardless of the full moon -- and you won't get your money back if you're disappointed.)

Island Adventures (tel. 787/741-0720) operates 2-hour nighttime trips in Phosphorescent Bay aboard the Luminosa, though not during the full moon. If the kids are into kayaking, they can get even closer to those glow-in-the-dark waters on a kayak tour offered by Blue Caribe Kayak (tel. 787/741-2522). In fact, Blue Caribe acts as a clearinghouse for all the island's watersports outfitters -- it's a small island, and virtually everybody is related to everyone else. That small-town casualness is one of the things that still makes Vieques a great place for traveling families, hot spot or not.

Contact: tel. 787/721-2400;

What: Biscayne National Park: Florida's Homegrown Coral Reef
Who: Ages 8 & up
Where: Homestead, Florida">Biscayne National Park is one of the least-crowded parks in America's national park system, probably because its main attractions are kinda difficult to reach. It's not a question of being remote -- it's so close to Miami, you can do it as a day trip -- but more about being hidden from view. Aboveground, you'll see only a no-big-deal strip of mangrove shoreline and 44 barrier islands, most of them mere specks off of South Florida's east coast. But beneath the surface lies the world's third-longest coral reef, an aquatic universe pulsing with multicolored life. All it takes is strapping on a snorkel and fins for kids to be able to cruise around this tropical paradise, encountering bright parrotfish and angelfish, gently rocking sea fans, and coral labyrinths.

The clear, warm waters of Biscayne National Park are packed with reef fish, rays, moray eels, jellyfish, anemones, sponges, even sea turtles and dolphins -- some 512 species, all told, in this 173,000-acre expanse. Not only that, an underwater trail identifies five shipwrecks about 3 miles east of Elliott Key; mooring buoys point the way to the wrecks, with waterproof cards attached to tell the kids what they're seeing. You can rent equipment at the full-service dive shop at the park's mainland entrance at Convoy Point, and if you don't have your own boat, you can take a 3-hour snorkeling or diving tour operated every afternoon by Biscayne National Underwater Park, Inc. (tel. 305/230-1100); you'll either stick to the bay or head out to the reefs, depending on the very changeable weather. Even beginning snorkelers will get a satisfying eyeful.

The mainland entrance is 9 miles east of Homestead, off U.S. 1; a small beach and marina is nearby, but the rest of the park is accessible only by boat, either your own or the park concession's water transport (tel. 305/230-1100). Few of the park's islands are even open to visitors; the two most popular are Elliott Key and Boca Chita Key, which can be reached by launch from the visitor center. Both islands have campsites (call the park ranger at tel. 305/230-1144 for information on permits and camping fees) and places to moor your boat; Elliott Key also has an interesting nature trail, and Boca Chita, once an exclusive haven for yachters, has some restored historic buildings.

If you prefer not to dive, take the wimp's way out and view the underwater sights on a 3-hour glass-bottom boat tour offered by Biscayne National Underwater Park, Inc., departing from Convoy Point at 10am. Reservations are almost always necessary.

Contact: Dante Fascell Visitor Center, at Convoy Point, 9700 SW 328th St. (tel. 305/230-7275;

What: St. John: Snorkeling on the Trunk Bay Trail
Who: Ages 6 & up
Where: St. John, U.S. Virgin Islands, the Caribbean

The first place my kids ever put a mask and snorkel into the water was down here in the U.S. Virgin Islands, and I'm afraid it spoiled them for more ordinary snorkeling experiences. I still have photos of them standing on the white-sand beach at Cinnamon Bay, along with the five kids of the other families we were traveling with, looking like an invasion party of aliens in their rented snorkeling gear -- eight breathing tubes sticking up like antennae, eight pairs of flippers shifting impatiently in the sand, and their masks making them look like eight frowning Cyclopes. We deliberately took forever getting that shot, just because it made them so antsy. Enough photos already, they wanted to get out in that turquoise water and start snorkeling.

Their snorkeling debuts took place where so many others have started out: at Trunk Bay, where the National Park Service has set up the National Park Underwater Trail. This 225-yard trail follows a reef where all the underwater features are labeled with signs 5 to 15 feet under the water's surface. Snorkeling snobs wouldn't be caught dead at popular Trunk Bay doing the trail -- they prefer more remote places like Waterlemon Cay or Salt Pond Bay or Haulover Bay, where the snorkeling's a lot more challenging -- but with children, Trunk Bay is just the thing. The signs help to focus young snorkelers' attention and keep them going, and it was extremely helpful for them to learn the difference between various coral structures, between a sea fan and an anemone. As for the bright parrotfish flitting by, well, no sign can be attached to something that elusive, but since the signs had made the kids more attentive snorkelers, they spotted the parrotfish all right. They were hoping for sea turtles -- hawksbills and leatherbacks are common in these waters -- but the turtles sensibly kept their distance. With kids, we were also grateful for Trunk Bay's other amenities -- flush toilets, a snack bar, and lifeguards.

We also just plain fell in love with St. John -- with two-thirds of it protected as Virgin Islands National Park, it's remarkably unspoiled, with lots of dense foliage and hiking trails and unruffled quiet, surrounded by expanses of clear, sparkling turquoise waters. It's what we'd always expected the Caribbean to be -- and now that we had the kids hooked on snorkeling, our island-hopping days could begin.

Contact: Virgin Islands National Park, Trunk Bay (tel. 340/776-6201;

This article is an excerpt from 500 Places to Take Your Kids Before They Grow Up, available in our Online Bookstore now. Author Holly Hughes has traveled the globe as an editor and writer -- she's the former executive editor of Fodor's Travel Publications, the series editor of Frommer's Irreverent Guides, and author of Frommer's New York City with Kids. She's also written fiction for middle graders and edits the annual Best Food Writing anthology. New York City makes a convenient jumping-off place for her travels with her three children and husband.

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