Divers have spent months exploring more than 200 small caves in the Yucatan peninsula, which they now believe to be the world's largest-known underwater cave.
The discovery of this 216-mile-long cave system is amazing on its own, but what they found hidden in the walls is believed to help scientists to solve a 500-year-old mystery.
The world's oceans make up approximately 70% of this planet, so it makes sense that they're a ton of secrets and clues to our past that have not been discovered.
It's also estimated that only 5% of the oceans have been explored, and what we've found in these deep, dark waters have already been super intriguing.
Take for instance the ancient underwater city of Pavlopetri off the southern coast of Greece. One marine geo-archaeologist discovered this thousand-year-old port town in the 1960s. They found pottery that gave clues to how humans evolved.
In eastern Mexico, underwater archaeologists traversed two linked caverns, known as Sac Actun and Dos Ojos, and found artifacts from an ancient civilization that hints at a mystery we've been trying to solve for centuries.