The Marietas Islands are an uninhabited archipelago about 35 kilometres offshore, now protected as a UNESCO biosphere reserve. They are most famous for the Playa del Amor — a hidden beach inside a sea cave, accessible through a narrow water tunnel that you swim or paddle through at low tide. The sight of a white sand cove open to the sky inside a rock chamber is the kind of thing that justifies the boat trip.
Beyond the secret beach, the islands are outstanding for snorkeling and wildlife. The waters around them support over 115 fish species, and sightings of manta rays, sea turtles, and schools of tropical fish are common. The islands themselves host 92 bird species including blue-footed boobies, which nest on the cliffs and are completely unafraid of visitors.
Access is strictly regulated: daily visitor numbers are capped, and you must book through a licensed tour operator. Tours depart from Sayulita (about 30 minutes by boat) or from Punta Mita. Book at least a day in advance in high season. During the winter months (December through March) it's common to encounter humpback whales on the crossing.