The Marietas Islands are a small uninhabited archipelago about 8 kilometres off Punta Mita, at the mouth of Banderas Bay. Designated a UNESCO biosphere reserve, they form one of the most important seabird breeding sites on the Pacific coast of Mexico: blue-footed boobies, brown pelicans, and frigatebirds all nest here in large numbers. The waters around the islands are equally rich, with reef systems where manta rays, sea turtles, and dolphins are regularly sighted, and they drew Jacques Cousteau to film here in the 1960s.
The headline attraction is the Hidden Beach — Playa del Amor — a crescent of sand inside a collapsed cavern, open to the sky overhead but completely enclosed by rock, reached only by swimming through a short tunnel from the sea. Its fame has come at a cost: access is now strictly regulated, with only 116 permitted visitors per day and entry limited to certified operators, so that the reef has time to recover from years of heavy traffic.
Most boat tours from Puerto Vallarta or Punta Mita combine snorkelling at the outer reefs with a panga ride past the cavern openings, rather than a landing inside. Even without setting foot on the hidden beach, the snorkelling, the birdlife, and the dramatic volcanic cliffs make the 30-to-45-minute crossing one of the best half-day trips on the bay. Bring a permitted operator, reef-safe sunscreen, and a tolerance for swells on the open-water crossing.