The ocean floor isn't flat or boring like you might think. It's actually full of amazing hidden features. For example, the Mariana Trench is a huge valley in the ocean floor. The bottom of the trench is the deepest place on Earth, over six miles below sea level. The ocean floor also has mountains so tall that they can be seen above water. For instance, Mauna Kea, in Hawaii, is even taller than Mount Everest if you measure from the ocean floor.