The spirit world is our earth but in a different dimension. The view of earth is different from within the spirit world.
The humans and other living beings cannot see you, but you can see them and you can also see the other beings from the spirit world who are floating around.
The spiritual dimension consists of three layers, the first layer where you arrive when you enter this dimension is the spirit gateway, which just seems to be floating in the air like magic.
Everything below you is concealed, but above is open. The layer above it, that you reach when you go upwards, is the upper spirit world. The guardians, spirit clouds and higher-level beings that guard this dimension reside there.
When you go downwards from the spirit gateway through the concealed ground, you will reach the mortal world, which is the human world. Faust and Yui were now in the mortal world.