The UnXplained (2019)

S04E03 What Lies Below?

More than 80% of the Earth's oceans remain unexplored, and in many ways, the underwater world is the final frontier. As new technology allows us to explore oceans and deep lakes more than ever before, what will we find? Will we discover profound secrets about the oceans? Underwater ruins that were lost for thousands of years? Or perhaps something even more extraordinary?