Cube world | SCHOOL ASSIGNMENT

In this school assaignment we have to make a 3D cube world by a 20 x 20 meter square.
We are each given a theme. mine is calm,alternate reality and underwater. This 3D project will either be textured or animated. you are allowed to do both. but knowing I wont be able to texture that fast I choose animation. besides I rather take my time for texturing. As an extra we needed to give it a little story. so, choose a temple made by humans and fish like people/ beings. In a world where they once existed. imagine the world being a 2015 world setting but long ago fish like people existed and now they evolved over time in more fish beings while still maintaining their intellengnce.