The Marieta Islands were originally formed many thousands of years ago by volcanic activity, and are completely uninhabited. The islands are about an hour long boat ride west-northwest from the coast of Puerto Vallarta.
In the early 1900s the Mexican government began conducting military testing on the islands because no one lived there. After years of scientific research and an intensive effort to legally protect this archipelago, first championed by Jacques Cousteau, it was finally pronounced a national park, Parque Nacional Islas Marietas, in 2005. The park spans almost 1,400 hectares.
On one of the islands is Playa de Amor, more commonly known as Hidden Beach. To reach this secluded paradise, visitors need to swim through a short tunnel, opening up into the stunning beach seen here. There are a number of tour operators providing day trips to this ecological marvel.
[Sources: Vallarta Adventures]