10. Vieques – Puerto Rico. Vieques is a Caribbean island off Puerto Rico’s eastern coast. It’s known for boat tours of Bioluminescent Bay (or Mosquito Bay), where microorganisms give the water a blue-green glow. It also offers secluded beaches and snorkeling. Wild horses roam the countryside, much of which is preserved as the Vieques National Wildlife Refuge. The Fuerte de Vieques is a mid-19th-century Spanish fort and museum.