On this episode, Mark and the crew are back at Grand Cayman Island… and on this adventure they're going night diving to ...

When sonar first picked up a massive, stair‑like object on the floor of the Baltic Sea, the image looked less like geology and more like a movie prop. The structure’s circular outline, sharp edges and ...

The ocean is still one of the biggest mysteries on Earth, and the deeper you go, the stranger it gets. Far below the surface, where sunlight can’t reach, lives a world full of creatures that look more ...