The highlight (for me) on Vieques is the magical bioluminescent water of Mosquito Bay! Ever been in a boat at night, with a virtual light show in the waters around you? Here on Mosquito, the shallow waters and mangrove clusters make a perfect home for protozoans -- called Dinoflagellates -- who breed in such density that the waters literally light up after dark!
You'll have your choice of outfitters to take you around the bay -- electric boat or kayak, expert biologist guide or family friendly. They're about $25 for 2 hours, and some even pick you up from your hotel.
The best of the island (#1 pick of TripAdvisor) is Abes! Check him out on YouTube:
http://www.youtube.com/watch?v=4-nBJBcorhQ&feature=player_embedded
Want to try a Paso -- or easy trot -- around the island? Horseman can join Billy The Kid (no joke!) throughout the heart of Vieques (787.741.2134) Or Esperenza Riding Company for a jaunt along the beach! Go in the morning or evening, to avoid the noonday sun -- it'll cost you $70 for 3 hours.
Into nature? The Kiani Lagoon has a wooden boardwalk with guided nature walks. These sacred waters, named for a native Indian Goddess, can be guided by Kiani Tours:
http://kianitours.com/?from=abes
Island fixture, Letty Perez, will show you wild horses, hermit crabs, cultural sites,
and the pride of Vieques, the Ceiba tree and its famous roots.
They are a looking-glass world, shimmering films of light and life that hide as much as they reveal. Such a thin slick of fresh water in the mountains might hold a nine-inch trout. But in saltwater, shallow water can yield a bonefish as broad as a bowling pin with the power to strip 100 yards of line. Or a man-size tarpon dressed in silver-dollar scales that gallops across the water like a bronco.
Here's the entire article, if fly fishing's your deal: http://travel.nytimes.com/2007/04/20/travel/escapes/20vieques.html
And when you get tired of running around, have your pick of some of the finest beaches in the Caribbean!
Red (the classic turquoise crescent)
Blue (with a sandbar out to a small key that's great for snorkeling)
Green (secluded by the coconut palms but watch out for afternoon sand flies)
or Black (the only untouched on the island!)
Try Navio, great for bodyboarding
or Media Luna, off of the Bun Bay beach road!
Top it all off with a food crawl in La Esperenza's kiosks for conch salad, coconut water, lobster, and all things fried!
"Pastelillos" are fried seafood dumplings
"Alcapurrios" are stuffed plantains
and Arepas are your standard fried dough (locals eat so much of these that they're nicknamed Areporos)
Or treat yourself to Bilis, a deceiving 5* open air cabana that's the highlight of the Malecon in La Esperenza! Start your meal with a namesake Amapola, or a glass of their famous Sangria. Salud!