How much of ocean floor is known to navigate?

So n the movie red October we have that famous chase through valleys on bottom of a sea. How much of that (underwater valleys)is really known by the navigation and or captain guys? Lots of ocean is so deep you don’t need to know everything but didn’t a sub ram an underwater mountain and crush its forward dome? That must be the ultimate submariner nightmare.

Also: i guess the knowledge is extreme but is it globally or are there still parts of the waterworld that are new, unchartered? And even if lits of ocean is very deep, there are also parts that are not so like north sea. That must be difficult to navigate underwater and not use active sonar?