East of Esperanza, Puerto Mosquito Bioluminescent Bay is one of the world’s best spots to have a glow-in-the-dark experience with undersea dinoflagellates. Local tour operators offer kayak trips or excursions on nonpolluting boats to see the bay’s microorganisms, which light up when the water around them is agitated. Look behind your boat, and you’ll see a twinkling wake. Even the fish that swim through and jump from the water will bear an eerie glow. The high concentration of dinoflagellates sets the bay apart from the other spots around the world (including others in Puerto Rico) that are home to these algae. The bay is at its best when there’s little or no moonlight; rainy nights are beautiful, too, because the raindrops splashing in the water produce ricochet sparkles that shimmer like diamonds.