Humans then build their buildings downward. It means that the 500th floor is actually the 500th basement.
Also, gravity acts weird here. If you try to throw something... It will float like a butterfly. If you drop something gently, it will be as fast as a damn cannonball shot by a supercannon.
There are three types of humans:
Caramelborn Humans are like the rulers. They have control over the environment of this planet.
Candyborns are great engineers. They build stuff from candy. Ranging from computers to high buildings.
Earthborns are from Earth. I have no idea how they got there.