The Marieta Islands (Islas Marietas) are a small group of uninhabited islands off the Nayarit Coast of Mexico. Thriving with uninterrupted marine life and thousands of bird species, the Hidden Beach of Marieta isn’t as easy to get to as you would first think.
Amazingly, this hidden beach isn’t a natural occurrence. It was formed in the early 1900’s as a target practice range by the Mexican Government during World War 1 and as nature took its course over the years, caves and caverns are now rich with marine life from the sea. Visit during the winter months when the water is at its clearest.
Source: When on Earth