What if..

[Crazierfox]

Very  Scary

Octlantis: the underwater city built by octopuses

But the discovery proves that Octopolis is not a one-off. Lacking any human object at its heart, its aquatic architects have constructed walls from clam and scallop shells, the remains of their former meals. Not only that, but the report’s co-author, Stephanie Chancellor, notes that these piles “were further sculpted to create dens, making these octopuses true environmental engineers”.

Biologists Have Discovered an Underwater Octopus City And They're Calling It Octlantis 
"At both sites there were features that we think may have made the congregation possible – namely several seafloor rock outcroppings dotting an otherwise flat and featureless area," says one of the team, Stephanie Chancellor from the University of Illinois at Chicago.

For some reason my mind went 

a different place