32 Offbeat Cruise Excursions That Go Way Beyond Sightseeing

8. Swim in the World’s Only Bioluminescent Bay in Puerto Rico

While the Caribbean is known for snorkeling and white-sand beaches, one of its most magical experiences happens at night. From San Juan or Vieques, an excursion to Mosquito Bay—the brightest bioluminescent bay in the world—lets you swim or kayak in waters that glow with every movement. The phenomenon, caused by tiny microorganisms reacting to movement, makes you feel like you’re surrounded by underwater fairy lights. Pro Tip: To get the best glow effect, visit during a new moon, when the sky is darkest.