The strip of sand in the Marietas Islands, off the coast of Puerto Vallarta in Mexico, is so secret that it cannot be seen from the sea or reached by land. Instead, you have to swim or float through a long underwater tunnel from the Pacific Ocean to get to it. The Playa del Amor, which translates as ‘the beach of love,’ was created by accident following a series of bombings by the Mexican government in the early 1900s.

The Marietas Islands were used as a military test site for several years until a group of environmentalists including the scientist Jacques Cousteau protested against the bombs in the 1960s. Bowing to pressure, the Mexican government not only put a stop to the tests but also turned the area into a national conservation area where fishing and hunting were banned. After remaining untouched for several years, the tide gradually washed up sand onto the water’s edge, creating what is now the beach. The sandy strip is now one of the most popular beaches on Instagram, but it remains relatively untouched by tourism because it is so hard to get to.