The oceans cover three-quarters of our planet, hiding a whole other world beneath the waves. If we could pull an imaginary plug at the bottom of the sea and, layer by layer, expose the majesty and mystery of what lies beneath, we would be astounded. This film reveals the longest mountain range (65,000 kilometers!); the deepest point on Earth; the largest stretch of flat plains; and psychedelic bioluminescent life forms that look like Hollywood aliens.

The ocean is the last frontier and images of the deep are only glimpsed in the lights of a submarine or ROVs (remotely operated vehicles), with most of this undersea world having never known the light of the sun. Leading international scientists and institutes in the field of oceanography and marine science join in this quest to lay bare the landscapes of the deep and share their experiences and ideas about what this mysterious world might look like.

Deep water corals that rival an urban skyline in size, a submerged canyon that is bigger than the Grand Canyon, a mountain range that runs for 65,000km - all these features have only been known in recent decades and while exploring these fascinating landscapes, scientists have discovered life forms that they had no idea existed - or could exist - in these bizarre, hostile environments.