If want to cross oceans you can work your way on merchant ships or pay a little bit if you want to just chill. Train is good in many parts of the world. And of course, if you have a solid bike, then there are few limits.
Crewing a yacht, if you have sailing, cooking, etc. experience, is also an option.
Trains in the US are more expensive than flights (for long haul routes), but in other countries, are a good deal. However, even in Europe, low cost carriers are price competitive with trains. Costs a lot more per minute, but the flight is much faster.
I'd imagine trains mostly go to the city centers while airports are more on the outer limits.