Fajardo has a small harbor with water taxis/ferries to the outlying islands, tour operators for scuba and the bioluminescence bay. Definitely sign up for a tour of the bioluminescence, which is best described as fairy dust-infused water. Laguna Grande, also known as Biobay, in Cabezas is one of the best spots. Its far from light pollution, quiet, and several operators offer varying modes of access into the lagoon. In case you want a smaller and even quieter experience Vieques and other outlying islands feature similar lagoons and may offer a more exclusive trip.