Sky World

I looked up into the bright morning sky and saw another world looking down on me.
Instead of the usual blue sky and clouds there were land masses and oceans staring down from on high.
It was difficult to judge the height above but several hundred miles probably.
I wondered about gravity and if it worked, as it must have done, to hold people and water onto the surface. Who were the people up there?
Was there a sort of giant letterbox shaped hole scooped out of the Earth?
If so, I would just be looking at the underside of it.
So, there must be a vertical bit, further in, joining the two bits up, like the inside edge of the letterbox.
If that was the case, I should be able to walk up the vertical bit, to the other bit in the sky.
Obviously there was a lot about the world I did not understand.
Sometimes I think I am mad.