Half the earth's surface is covered by water more than a mile deep, but most of this watery world is a mystery to us. In fact, more people have stood on the surface of the moon than have visited the deepest spot in the ocean. Come along as we travel down, down, down from the surface to the bottom of the sea. Along the way you can see jellyfish that flash like a neon sign, creatures with teeth so big they can't close their mouths, and even a squid as long as a bus, which battles to the death with a sperm whale, the largest predator on earth. It'll be a journey you won't soon forget.