Is This A Possible Sunken City off the Coast of Australia or Possible E.T.Base??

I Like to scroll around sometimes on Google Earth and see if I can find New things that haven't been Photoshopped out by the Powers that be!
And this time I found a structure that has 4 straight Lines in the shape of a Square, off the coast of BUNDABERG Australia, that has a Corner 2 Corner Diameter Reading of 42 Miles, or 30 kilometres.
It also has Height, and a Plateau like Platform at the Top!
I've taken Photos all the way around this structure for everyone to peruse over, you be the Judge for yourselves whether or not this is a Sunken City, Or Possible E.T. Base!