But we can assume there are a few ways, like the sea train? Perhaps the government has some undersea motorway built? Vegapunk is probably the person that does this for them.
Agreed, since there are Sea Trains in Film Z going from Dock Island to Secon Island.
And Water 7, to an Shift Station in an island not too far from Water 7. But that's only a few.
And Tom built tracks to go the islands: St.Poplar, Pucci & San Faldo. Again just a few.
There could be many ways to travel, maybe there are giant birds, like the ones Chopper used for citizens? Those were tamed by the WG? Maybe there are special ships guarded by marines so that rich people travel in peace? I doubt ordinary folk and poor travel much tho.
I like these theories I'll admit. The birds one being a bit unlikely but special ships guarded by Marines to escort the rich would make a lot of sense.
But I'm certain that the poor travel though.
I mean, how do they trade and stuff? All islands need to trade surely?
How else do people leave their island and join a marine base?
Or do the Marines go around visiting islands asking who wants to be a recruit?
The concept of travelling in One Piece really bothers me lol.