(SPOILER)It's most likely to represent the fallen Zanarkand. As far as a practical purpose, there is the City and the Tower of the Dead inside of Sin. Sin in this case is like a giant floating Farplane for the Fiendish unsent.
(SPOILER)It's most likely to represent the fallen Zanarkand. As far as a practical purpose, there is the City and the Tower of the Dead inside of Sin. Sin in this case is like a giant floating Farplane for the Fiendish unsent.