The structure, estimated as being between 3.5 and 11 miles across, was spotted on Google Earth in the Pacific Ocean just west of Mexico.
A video about the discovery uploaded to YouTube has drawn vast speculation about what it could be, including an ancient sunken city, a bizarre UFO, or even an alien base.
The "discovery" was made by Argentinian Marcelo Igazusta.
Clearly the End Times are upon us. This MUST BE the lost city of R'lyeh!