User blog comment:Balbal1/End of the Grand line/@comment-24769684-20160322184906

There isn't a Road Poneglyph on there, otherwise someone would know where it was (unless no one's ever managed to reach the end of the route, which I doubt).

I can't really think of anything off the top of my head of what the last charted island could be, but I have two theories. One is that it's the wildest island in the world in terms of climate, as the fact that EVERY log pose goes to it hints that it should be special in some way.

Also, I wouldn't be surprised if there's a HUGE Marine presence on the island (G-1???) It would be a very logical thing for them to do.