This remote thin, white-sand beach has one of the best snorkeling areas in Puerto Rico thanks to a barrier reef that almost encloses the beach's waters; you can snorkel on either side of it by swimming through the boat channel – look for the floating white marker – at the right-hand side of the beach. But be warned: water taxis and local powerboats cruise this channel, and swimmers have been hit.
To get to the beach, follow a path through an opening in a chain-link fence on the western side of the parking lot at Playa Flamenco. A 15-minute hike over the hill brings you to a tiny beach. Continue north from here, crossing the narrow peninsula, and head down to the sandy basin and shade trees of Playa Carlos Rosario.
For truly spectacular snorkeling, continue working your way north along to the beach for about a half-kilometer to a snorkeling site called the Wall, which has 40ft drop-offs, huge sea fans and rich colors.