Located in the Yucatan Peninsula in Mexico, there’s a secret underwater river called Cenote Angelita (Spanish for Little Angel) that can be found after a 10 to 15 minute drive south of Tulum. The cave is around 55 m deep and the first 30 m is filled with fresh water. After the layer of fresh water comes a thin layer of hydrogen sulfate, below which is 25 m of salt water.
It is arguably the most unique formation of this kind: a thin layer of hydrogen sulfate separates the saltwater from the fresh water above it, allowing scuba divers to swim along this underwater creation, which looks a lot like a regular river would on the ground. There are even fallen trees and leaves on both sides of the “shores”, making this seascape look all the more surreal!