Vana'diel

Vana'diel Versions
Final Fantasy XI
Grandmasters

Vana'diel (ヴァナ・ディール [vana'diel] in Japanese) is a huge world consisting of at least 6-7 continents. The two continents of Middle Lands called Quon and Mindartia (and are central to the game), the near-eastern continent of Aradjiah, the far-eastern continent (which might be connected to or be the same as Aradjiah), the western continent Ulbuka, the northern continent Rhazowa and the southern continent Olzhirya. In addition, there are various smaller islands that aren't quite big enough to be categorized as continents, such as Zepwell and Tsahya.

Many great nations exist on Vana'diel, and not one seems to have supremacy over others. The closest that any come to this are mentioned in passing only, such as 'the great northern Elvaan homeland' or 'the great home nation' of the Mithra (to the north and south respectively), but it is unknown if these are truly unified countries set on the northern and southern continents or simply countries that occupy parts of said continents. It does appear, however, that the Grand Duchy of Jeuno in the Middle Lands is widely acknowledged as a center of trade and commerce.
Distances on Vana'diel are quite vast, and as such cultural differences and level of technology varies greatly by area you're in.

Vana'diel is an interesting case in that it has many alternate courses of history that are known to us. The main one of these is the timeline/dimension of the world that the player starts out in in FF11 and spends most their time in, as it is actually a dream world of the goddess Altana after the true timeline succumbed to darkness. This story is explored in Wings of the Goddess.
Another alternate Vana'diel is Abyssea, although this one's history separated from the other two Vana'diels' in the far distant past, far enough that it is almost unrecognizable to the residents of the other two. It is almost overrun with demonic/Empty beasts. Its story is further explored in Vision of Abyssea, Heroes of Abyssea and Scars of Abyssea.