Río Secreto (or Secret River) is a semi-flooded limestone cave system near Playa del Carmen, Mexico. There are 38 kilometers of caves in the system, of which approximately 10% are used for ecotourism. Currently, Río Secreto is protected as a nature reserve.

As with other caves in the area, local Maya have known about the cave system and used it for ritualistic purposes hundreds of years ago. Various artifacts created by the Mayans have been recovered from the cave system, including religious altars, cave paintings, and a vessel dating to the postclassic period.

In 2004, a farmer discovered the cave after chasing an iguana into an entrance. A group of speleologists and divers from the area visited to map the caverns, defining routes and establishing their relationship with each other. An agreement was was formed with the owners of the land to create a conservation plan. Formal exploration of the cave began in December 2006 and ended in September 2007, and the cave was opened to the public as a guided tour in April 2008. In 2016, Río Secreto had 104,000 tourists.