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Raftel’s Location Theory
Raftel was first mentioned by Crocus, It is the last island of the Grand Line in which by assumption, One Piece is hidden, even Crocus supposedly didn’t know where Raftel and One Piece was hidden.

But actually, Crocus did know the location of Raftel. Naturally, Raftel is the final destination and the location of One Piece. That’s simple, just get to the final island right? So why nobody except Roger reached it? Because the island of Raftel is hidden.
Let’s look at some statements from the manga first:
We had been introduced to undersea volcanoes
Winter Islands
A very talented navigator
A very formidable ship
And Ship Coating
So, what’s the point of these things?
It’s the “way” to get to Raftel. The reason why no one reached Raftel is because Raftel is a “Rough Tale” or a legendary island. it’s an island that exists if you are willing to face dangers it presents.
Raftel is a floating, man-made island in a sea that is hidden underground or more specifically, inside a land mass. It is a “Raft” Island, reason why no log pose can detect it.
A pumice raft is a floating raft of pumice occasionally created by ocean-based or near-ocean volcanic activity. Biologists suggest that animals and plants have migrated from island to island on pumice rafts. Astrobiologists have hypothetically linked pumice rafts to the origin of life.
But where exactly is Raftel located?
Remember the proverb: “Sometimes what you’re looking for is right in front of you?”, it exactly applies to where Raftel is hidden.
Are you familiar with a pirate treasure map? Notice that the big X on every map is where the treasure is hidden.
Now, look at the One Piece World Map. Do you see the treasure mark?

Don’t see it? Take a closer look, the X is where the treasure is.

It’s right there. Raftel is inside the Reverse Mountain.
But that doesn’t mean that anyone can be lucky enough to stumble Raftel one way or another right. It’s just the “way” to Raftel. Of course we need the “fare”, “guides” and “drivers”.
And don’t you guys notice that though there is a way to get down to the Grand Line, there is no way to get back up on the other side? unless you’re in the Marines or a very strong pirate like Mihawk, going back to the 4 blues means you will have to backtrack until you reach the entrance to Reverse Mountain again.
And I can’t imagine how you can climb back up that mountain, so basically there’s no turning back to the four Blues.
This is where Luffy’s ability to hear “the voice of all things” comes in handy.
By the way, don’t you guys notice something with the former members of Roger Pirates? Luffy met Shanks in his village, Crocus in Twin Capes and Rayleigh in Sabaody Archipelago. Let’s consider Shanks, Rayleigh and Crocus as the “guides”.
What does this all mean?
You guys must have observed that Crocus and Rayleigh settled in a place where ALL pirates must go through right? Twin Capes is the place where pirates needs to go through when entering the Grand Line and Sabaody Archipelago is where pirates must stop by to proceed to Fishman Island. Isn’t that weird? Like they intended to be there of all places.
And isn’t it weird that out of all the people Shanks knew, he gave the Straw Hat to Luffy?
My guess is, Shanks was the “guide” and caretaker of the Straw Hat who was appointed to search for “The One”.
Seeing Luffy as “The One” they (The Roger Pirate Remnants) are waiting for, Shanks gave Luffy Roger’s Straw Hat to give sign to the other “guides”, Crocus and Rayleigh (and Gaban perhaps), that the successor to Roger’s will had arrived.
If you guys remember, Shanks stayed at Fuschia Village for years, I assume Shanks that time was on a mission to find the “D” to follow Roger’s will, prior to that, I believe that Shanks first tried to “test” a guy named Marshall D. Teach, but that guy turned out to be a traitor, note that Shanks met Blackbeard before Luffy.
Then harboring at Fuschia Village, Shanks met Luffy, another “D” and tested him, in which Luffy passed, so to assure that Luffy would come and become a pirate and ultimately arrive at the last island of New World where Shanks will wait, Shanks entrusted him the “Straw Hat” as a “fare” in which everyone close to Roger that will act as a “guide” will identify.
Roger’s Straw Hat is the “fare” the “guides” had been waiting for to lead Luffy to Raftel.
I do not know if Shanks had no interest in One Piece from the start, but one thing is fair to assume: he knows how to get there. But maybe he can’t or he knows they cannot reach it, or he simply just want Roger’s will to be fulfilled.
So, in order to carry the will of Roger, I believe Shanks (and other members of Roger Pirates) have all decided to wait for “The One”.
Here we see Crocus and Rayleigh expressing how they think Luffy is “The One”.

It had been said that the Roger Pirates had been gone for 1 year before Roger finally gave himself in.
Probably, Roger planned everything and then instructed his most trusted crew members that the will to change the world should be passed to the next generation because his days are numbered and he cannot finish the job because of his conclusion on the Poneglyphs and because he lacks what Luffy “got” right now.
Roger turning himself in, probably is his best way to be a fire-starter and create a new age of Pirates. (Like what Dr. Hiluluk did, with Isshou 20) and using One Piece as the prize so people would get interested.
So the “guides” jobs are fulfilled right? Not yet.
Their job is not yet done and in fact all the “guides” have not been found yet. There’s still one: Scopper Gaban.
Where would the crew meet Gaban?
If my calculations are correct, the crew will meet Gaban, like Rayleigh and Crocus, in a place where all paths converge to one, and in Grand Line, there are only 3 of them: Twin Capes, Sabaody Archipelago and Raftel. Scopper Gaban is most likely on Raftel.
The place where the different paths will converge into one once again, but this time, only one group will reach Raftel and Gaban is the guard of that place in case someone not worthy escapes Shanks’ station.
The “guides” job would be complete after the right one reaches Raftel.
Shanks roaming around the world looking for the guy who would bear the Straw Hat.
Crocus stationed in Twin Capes so he can relay the information to Gaban that the one they are waiting for had arrived.
Rayleigh making sure that “The One” would reach the New World safely.
Shanks waiting at the final island of the New World, expecting that the invested promise he put on “the Straw Hat” will really arrive.
Shanks being the guard to stop anyone who would go after “The One”.
Scopper Gaban keeping guard of One Piece and Rio Poneglyphs until “The One” arrives.
I suppose Gaban is this guy chilling with Crocus in the Twin Capes since he just needs to get out of the Reverse Mountain.

Wait, what? Get out of Reverse Mountain? Going in is extremely hard, how the hell can you get out of that place?
Same way how the Thousand Sunny will get out after getting to Raftel. By coming out of the center of Reverse Mountain, like this:

And I think it had been foreshadowed with the Strawhats meeting whales on the key points of their journey, twice: after entering the Grand Line and after entering the New World.
When they enter Raftel, it would be like meeting a whale, the whale, though, is the Red Line and Reverse Mountain itself, because Raftel is like being swallowed by a large whale and blowing you out of his hole in his head. The frenzy entrance to Reverse Mountain to Grand Line and being sucked out by a White Strom also appeared to me as a hint of the crazy ride out the Reverse Mountain.
Basically, going out of the Reverse Mountain is as crazy as entering the Knock-Up stream. (now that I thought about it, entering Skypiea also gave foreshadowing of being like swallowed by a whale and going out like being blown upwards) and Luffy’s arrival (being sucked in by a whirlpool and coming out of a barrel upwards).
That’s right, going out of Reverse Mountain is the same principle as of the Knock-Up Stream, the only difference is, there’s a twist.
Not only is the Reverse Mountain a winter island, which is why it pushes the water out to grand line, It also has an underground volcano inside it, that produces a whirlpool that creates strong upward currents for the four Blues’ oceans.

Here’s the idea of Knock-Up Stream, this is what’s right below the hole of the Reverse Mountain I assume, an underground volcano.

Not to mention that a volcano got a crater, so it creates a whirlpool underwater, It had been shown in the series how a hole in the seafloor affects the flow of the currents.
So, to simplify the explanation of water currents throughout the series, unlike the Knock-Up Stream that lasts up to only 1 minute, I’ll assume that the Reverse Mountain is a continuous flow of warm water (undersea volcano) and cold water (Reverse Mountain being a winter island) reason why it creates a never ending whirlpool (also because the undersea volcano inside the mountain got a crater which create whirlpools) and a Geyser-like reaction in the middle.
It produces a current that pulls in and at the same time, pushes out.
Here’s an illustration:

That’s why a very formidable ship and a talented navigator is required. And this is how the crew will get out of Raftel.
Also, did you guys notice something? The Reverse Mountain pulls in the waters from all the four Blues, and Nami already stated that you can get either dragged down or get through down the Grand Line.
So it’s logical to think that since there is an ocean inside the Reverse Mountain and since ships can get caught in the mountain’s current, It is definitely possible that fishes gets caught in it too.
As an evidence that fishes get caught in the Mountain’s current, here’s one that came from South Blue and got through to the Grand Line:

Waters from all four Blue seas meet in Reverse Mountain, so do the fishes: All Blue. All Blue, the legendary ocean is the ocean inside the Reverse Mountain.
As soon as the crew reaches Raftel, Sanji will fulfill his dream of locating All Blue.
And as soon as they come down to the Twin Capes again, Brook will fulfill his dream of meeting Laboon.
Now that we discussed how would they get out, let’s first see how the crew would find Raftel.
So there’s no entrance to the other side of the Reverse Mountain.
Earlier we saw the panel that says the Reverse Mountain is a winter island right? Well obviously, the water around winter islands is obviously cold, and these part of the ocean produce “downward currents” especially in the deepest regions.
Well, it’s not that hard to do, just coat the ship and submerge, and a very good navigator will get the job done.
But here’s the tricky part, because if the entrance to Raftel is just under the ocean in line with the Reverse Mountain, some other pirates with a good submarine like Trafalgar Law or good navigator like Blackbeard should’ve already found it.
So while I do believe that entrance to Raftel is by going under the ocean and locating the entrance, I’d like to believe that the way to Raftel is somewhere were no ship would think of submerging to – the Calm Belt.
The entrance to Raftel may be in the Calm Belt along the Red Line near the Reverse Mountain in the end of New World, under the ocean.
I believe that the “entrance to Raftel being in Calm Belt” idea is proven on the events before time-skip when Silvers Rayleigh swam trough the Calm Belt.
Of course, no other pirates or person would try this, even if they are as strong as Rayleigh, because they don’t know that Raftel’s entrance is there.
So, how the hell could they submerge in the Calm Belt?
You guys remember the Calm Belt and the Sea Kings the Strawhats met before they even entered the Grand Line?

Well what do you know, they were in Fishman Island too.

They went through the Red Line. It’s one thing that they can go through the Fishman Island, but I believe that there’s an entrance in the deepest regions of Calm Belt along the Red Line on the entrance to Grand Line too because Calm Belt is supposed to be the Sea Kings’ lair.
You guys remember that Fishman Island was 10,000 meters deep right? I think Calm Belt is deeper or at least as deep if its the Sea Kings’ lair.
As stated by Brook earlier, there are certain group of species that can submerge in deepest level of the ocean, and that includes the Sea Kings.
first of all it’s too dark and only massive fishes can go there, and Fishmen can probably go there but it’s either they never leave their kingdom in the Fishmen Island or even they fear the Sea Kings to go there.
And it’s the Calm Belt, no one probably ever goes there. Not even Fishmen, and even the Marines needed kairoseki (sea stones) to cross the Calm Belt.

So what happens when other fish/sea creatures that can’t submerge that deep and get lost by going into this dark and deep entrance? The whales that can only be seen in West Blue will give an example:

They are scarred all over, they got through but they had been severely injured. Well, unless you have someone in your crew that can “hear the voice of all things”.
In the first few panels, we can see that the Sea Kings are hinting that Luffy will develop this ability later on in the series, and in the last panels, comparing him to Roger.

I did mention about the “way”, the “fare” and “guides” to get to Raftel, but the most important one is to get the “drivers” to help you – the Sea Kings.
As stated earlier, submerging to the deepest regions of the ocean is a hard thing, but most probably it’s extra hard submerging into the Calm Belt.
First, the currents deep down the Calm Belt probably is the wildest, heaviest and most unpredictable current in all of the oceans. Second, it is infested with Sea Kings. Third, one cannot simply dive into the Calm Belt.
The ability to “hear the voice of all things” is the ability to “understand” the will, history and feelings of a being, living and none even without speaking in tongues.
Note that the ability to hear “the voice of all things” and Poseidon’s ability are two different things: Poseidon can fully control, speak and manipulate Sea Kings, while Luffy’s ability is just to understand “their voices”.
Chopper, Jinbe and Camie’s ability to hear and speak some animals are also different, it’s their natural ability due to them being half-animals.
Isn’t it weird that Luffy befriends too many animals? It’s not just a running gag. Luffy is actually unlocking his ability little by little.
And Luffy got this, although unlike Roger, Luffy is not fully awakened and aware of it. I assume Roger was.
The reason why Roger can understand and write on the Poneglyph in Skypiea even without the knowledge about it, but nevertheless, whenever Luffy becomes aware of his ability of hearing the “voice of all things” it will help him understand the calm waters of Calm Belt that calls his ship to go and submerge underwater and find the entrance to Raftel.
And the ability to hear “the voice of all things” will invoke the aid of Sea Kings, guiding and keeping their ship safe in locating the entrance to Raftel.

So now, with the crew having reached Raftel, Luffy fulfilled his dream, One Piece is located there, rightfully guarded by the final “guide” Scopper Gaban.
The Rio Poneglyph is also there. Robin fulfills her dream of locating the Rio Poneglyph.
Thousand Sunny reached Raftel as well. Franky’s dream is fulfilled.
Chopper may discover a special plant on Raftel that turns out be the Panacea (medicine that can cure any thing) which he would use later. Chopper’s dream fulfilled.
Nami can draw the final island and finally fulfill her dram of drawing a map of the world.
Just one last thing, if you need more evidence about the location of One Piece, it is also hinted in the logo of One Piece logo itself, read this illustration for the detail:

Shanks is another word or term for “anchor” which is at the end of the logo. Shanks is waiting for Luffy at the end of the world.
All rights go to the maker of this theory.