Answer:
I am a portal to another world which you cannot enter. Only you can see me but I can't see you.
I have feet on my head
By Moon or by Sun, I shall be found. Yet, if there's no light around, I am undone. What am I?
My days are numbered.
I don't have eyes, but once I did see. Once I had thoughts, but now I'm white and empty. What am I?
Brings the sky a lot closer.