That's a pity - the first thing I felt upon reading about the Ocean of Fragments was a desire to see what was past or below it. Something about declaring the Ocean to be the uttermost nadir just doesn't sit right with me - It comes across as too human and too modern in conception to be a true edge of reality.
To quote Book of the Dead:
"Finding the Ocean of Fragments isn't easy. It's a long away from the surface. This Dominion lies deep within the Underworld, past many of the other realms that reflect (or at least call to mind) human notions of death and what comes after. Considering the appearance and effects of the Dominion, it might well be the
deepest of any known realm. Certainly, the travelers who have found the Ocean and returned report feeling a sense of finality when touching its waters, as if they have truly
arrived, and no further progress is possible."
Of course, on page 11 when it discusses the general topography of the Underworld, what it says about what is 'below' the Dead Dominions such as the Ocean is, "... well, who knows? What lurks beneath the Dead Dominions is subject to mystery. Is it the Abyss? Another world? Absolute oblivion? A Land of dreams? None can say, because if anybody's ever made it that deep, they damn sure didn't come back up."
I mean, the fact that the Admiral's ship varies with the times is nice, but it's still a bunch of spooky skeleton sailors and an admiral on a boat, with a sea monster in the water. I just wanna somehow bring in a submarine (or at least an atmospheric diving suit / some other way of going under without getting wet), sneak past the Leviathan somehow, and find the REAL bottom.
The Maritime Law: Only the
Freighter may sail these waters.
Good luck with that.
You're also not thinking correctly when it comes to this. You don't go DEEPER by digging, you go deeper by moving forward. Even if something is 'past' the Ocean, it would be found in the same way one would find the rest of the underworld. You would cross the Ocean, which means getting the Freighter to ferry you, then you would have to swim ashore, then you would have to cross the next River.
Also, the Admiral is sold as this ancient, mysterious figure despite being entirely killable in a few different ways and the fact that, y'know, the actual first humans wouldn't have had much knowledge of naval organization, sailing, or the existence of boats. But you can't really argue "he's just a latecomer pretending to be something primordial" when four of the twelve laws of the Ocean relate to him or his boat unless you take as a given the entire Dominion is a false bottom.
Or, the Admiral is a Title, not a Person. Like 'The Captain' of the Flying Dutchman in Pirates of the Caribbean. Similarly, what else is more the ultimate 'source' of death, then where life began, the Source of Life, if you will. As well, what place has seen the most death in all of history, probably that place that life started in.
And, you're forgetting your WoD Cosmology / Mythology. In nWoD, Atlantis was the FIRST CITY. An island where Dragons lived and died, guarding the source of all magic until their time had passed. And then it was discovered by Man.
Also, you're just plain wrong. Humans have been sailing since forever, it's how we managed to populate basically the entire planet, even remote islands, before the 'great age of sailing'.
From whence we came, so do we return. And beyond that horrible expanse that seeks to rip from us all that we are and either make us into new men or leave us dead and forgotten, lies a land of myth. A realm from which none might return and speak of what they have seen.