If getting wet is your purpose, however, there's no better place to get drenched than the bioluminescent bay, a body of water inhabited by tiny organisms that shimmer like miniature disco balls when agitated. Only a few countries in the world (e.g., Jamaica) possess the rare and beguiling bioluminescent bay, and Puerto Rico has three of them—in La Parguera near Fajardo (southeast), in the town of Lajas in the Porta del Sol region (west), and on the island of Vieques (off the eastern coast).

"If for any reason you fall into the water," Jose Cintron of Island Kayaking Adventure announces during the 90-minute drive from San Juan to Farjardo, "you will be glowing so much, like Tinkerbell."

The protected bay is best accessed by two-person kayaks, in which paddlers steer through a snaking, narrow channel lit only by the moon and fluorescent bands attached to the boats' bows. The ride is tranquil and meditative, unless you hit a traffic jam of returning kayakers or slam into a mangrove branch hiding in the shadows.

Kayakers typically adhere to a "No Swimming Allowed, but Falling Out is Okay" rule. But here a different logic applies. To really make the little buggers' shine (especially when the moon is out), you have to stir them up some. The best way is…men and women overboard!

On a summer's eve, the water is calm and warm, and with each sweep of the hand, a small patch of bay sparkles like millions of diamond chips. Swimmers make glow angels and toss the organisms around like shimmering confetti. Then, they are ordered back in the boats.

On the paddle back, the dinoflagelletes' light dims, then goes dark. Much like the final Puerto Rican adventure of the night.