Oceans, openly dividing one land from another. The coastline covered up with foam, clashed at the big, sharp cliffs, that calls for stunting mortals living dangerously.
I love the ocean for the big secrets it's preserving and protecting with waves and creatures we might not have even laid eyes on before. Sea monsters roaming down in the dark abyss never to see daylight.
When the ocean feels threatened, it creates storming grey storms, with purpose to destroy, and the act of Mother Nature will travel around doing precisely what it's purpose is. Some might be afraid of the ocean's unrevealed under layer. Afraid of what they don't know. It probably being more daunting if known.
The earth we live on contains an everlasting amount of darkness that haven't met human eyes before. This is why I find oceans so incredibly, implausibly interesting. Because the ocean as we know it, might not be anywhere alike the ocean that is.