70% of the Earth's surface is water. Arthur C. Clarke famously said: "How inappropriate to call this planet Earth when it is clearly Ocean". As of 2023, less than 25% of the sea floor has been mapped. Less than 10% of the ocean has been explored. In that tiny amount of exploration, we've found things that defy logic and challenge history — sunken cities, ancient monuments, and objects that look like they're from another world.