Ok, thanks for the correction and the info. How did it sink?
The Redguards blew it up because they didn't know how to use the tower properly.
And just a note, the entire thing didn't sink, most of it did, but a chain of islands still remain.
Just another note, by "blew up" mean they destroyed the tower and thus the local reality of the continent, causing it to degenerate and thus sink into the sea.