This was the Nine Seas God World, one of the Three Great Daoist Societies of the Ninth Mountain and Sea!
It had existed for tens of thousands of years, stretching back into ancient times, seemingly eternal. Apparently, it had existed for as long as the Nine Mountains and Seas themselves. People who practiced cultivation here for a significant amount of time, and then left for the outside world, would experience an explosive rise in their cultivation base.
In all of the Ninth Mountain and Sea, the only sect which was so amazing that they could practice cultivation in the Ninth Sea itself, and even lower their sect to the bottom of the sea... was the Nine Seas God World!
Because of cultivation practices like that, it was no exaggeration to say that it was a God World. That was even more so when you considered the power of Heaven and Earth which existed there. In all of the Ninth Sea, this location had the most terrifying concentration of it.