A bunch of architects want to build a $26 billion underwater city in Tokyo - take a look

Earth as we know it might not last forever.

If $4 rise triggers flooding in our cities, if climate change $4 to grow food for billions of people, or if there's some other as-yet unthinkable apocalyptic disaster, humans will need a new home.

The architects at $4, a Tokyo-based firm, want to build underwater cities that they call Ocean Spirals.

There are no concrete plans to construct an Ocean Spiral, which project leader Masaki Takeuch estimates would cost $26 billion. But the renderings are certainly fantastical.

Check them out below.