User blog comment:Blackendedsoul/What's stopping him?/@comment-4754162-20120615170110/@comment-4754162-20120616153426

About Raftel, not only Kuma and Blueno but perhaps the old folks of Weatheria, the Rosy Riders, Lafitte, Marco, Enel, Kizaru, Kuzan, Shiki and the likes (who can either fly or travel across the ocean) could have gone over to Raftel using their own specific ways respectively, no...

Like how Roger inspired pirates with the great treasure One Piece (hence the Pirate Age), if the marines wanted to do something about this, they could have just sent Kizaru or Kuzan towards Raftel, grab whatever shit One Piece is and declare to the world that marines have it already and all pirates will no longer be motivated. Ah, of course the key question remains... the unknown location of Raftel...

So in weighing all these in, I'm guessing Raftel could not be accessible by normal conventional means, Granny-chin could be right - its at another dimension or say its at Davy Jones' Locker (remember that place in Pirates of Caribbean?)