Massive underwater structure 180 km off coast of Antarctica

A huge underwater structure 180 km of coast of Antarctica shows among other objects, huge walls. 

Suppose, this enormous structure are the remains of a huge ancient settlement or base that is now submerged under water, then who built it thousands of years ago? 

Coordinates: 63°59'56.79"S 118°43'44.48"E 
Special thanks to Frederick Johnson