The Dustless Sea isn't located in any major world; it simply drifts within the cosmos, a planet of pure water. The entire planet is a vast ocean, limitless and without horizon.
Not even a small island exists within the sea, and there isn't such a thing as a seabed.
If one's Tao cultivation is sufficient, they could plunge from the sea surface on one side and emerge from the water on the other side—at least, that's the theory. But so far, apart from the Wasteland Ancestor, no one has managed to reach the core of the Dustless Sea on their own.
Besides water, there is nothing else in the entire Dustless Sea, at least as far as the eye can see.
The Wasteland Ancestor has been Suppressing the Dustless Sea for an unknown number of years. It has become a spectacle in the All Heavens and Myriad Realms.
