Spira

Spira Versions
Final Fantasy X
Final Fantasy X-2

Spira is a largely oceanic world that has long since lost the peak of its civilization. It presumably has one white moon, and appears to have only one main continent along with several islands surrounding it. The rest of the world as far as can be told is ocean, and very much of it.
There is what appears to be a separate dimension attached to Spira, what is known as the Farplane. It is said to be where the souls of the dead go, although this is unconfirmed. Some say that what is seen on the Farplane is merely reflections of what you want to see shown by the pyreflies.

Thousands of years in the past, Spira was ruled by two advanced civilizations at war, those of the northern people of Zanarkand who used the power of summoning, and the people of the south who used machina. When it became apparent that the machina-wielding people would win, the people of Zanarkand gathered for one final great act of summoning. Their leader Yu Yevon became the focal point and became Sin, who destroyed all the civilization on Spira. Only small settlements could survive under Sin's rule, for larger ones attracted his wrath. The people who used machina eventually came to believe that they were punished for their use of machina, and based their religion around that. Summoners went forth periodically to banish Sin from the world, but the peace they brought was never lasting, and Sin returned just like before, and every time the peace brought by the summoner was shorter than the last.

Eventually, the summoner Yuna and her friends broke the cycle and defeated Sin for good. Since then, the culture of Spira has flared up anew, with people rejoicing over the absence of Sin, even to excess.

Spira has been confirmed to exist in the same universe as Gaia in FF7. Travel is possible between the two of them in spaceships of some kind.