As rising sea levels pose an increasing threat to island dwellers, a Japanese civil engineering company has come up with an ambitious solution: an underwater city.

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The proposed Ocean Spiral would consist of a large sphere just below the surface and about 546 yards in diameter, occupied by homes, businesses, and hotels.Under that, a spiraling structure leading down to the sea floor would provide a way for scientists to extract resources for energy.In a statement to The Guardian , Shimizu Corp spokesman Hideo Imamura said, "This is a real goal, not a pipe dream."Shimizu's vision for the self-sustaining underwater city involves converting carbon dioxide into methane with the help of micro-organisms, as well as a process called ocean thermal energy conversion.Based on the company's plans, Ocean Spiral would cost 3 trillion yen, or over $24 billion USD, and take five years to construct, though Shimizu acknowledges that the technology required to undertake such a project isn't available yet."The Astro Boy cartoon character had a mobile phone long before they were actually invented – in the same way, the technology and knowhow we need for this project will become available," said Imamura.Shimizu estimates about 15 years until then.In a few decades, maybe a real-life Rapture could be a possibility.

Chloi Rad is a freelance writer for IGN. You can follow her on Twitter at @_chloi