This south Vieques beach might not sound like much, but it's one of travelers' favorite experiences in Puerto Rico. During the day, Bioluminescent Mosquito Bay is your stereotypical Caribbean hideout, but at night, the waters emit a blue glow from the organisms, called dinoflagellates, that live there. More than 600,000 bioluminescent dinoflagellates live in each gallon of bay water, and recent travelers have been amazed by just how much visibility these tiny creatures provide.

Avoid visiting the bay during a full moon; the microorganisms aren't as visible then. Also aim for a quiet approach. Recent travelers recommended going out in a kayak to get the full effect of the glow and to prevent disturbing the dinoflagellates.