Can anybody remember this?

[JP]

The story concerns a boy & girl who leave their village looking for adventure and fabled 'old' city. As far as I remember they were living in a post apocalyptic world.
Eventually they find the city. One detail I remember is that they see old movie posters outside a cinema.
At the end of the story, spaceships land. Humans who left centuries ago have come back to warn all poeple that the earth will be destroyed and that they must be evacuated.
This sounds like two stories... Maybe I'm remembering incorrectly...
Hopefully somebody knows what I'm talking about.

[JP]

OK since nobody seems to know, I'll add two more details. But I'm not at all sure if I'm correct about these - which is why I did'nt include them in the above post.

1. I think the story/book was written by Isaac Asimov...
2. I seem to remember that the world was going to be destroyed by a 'Goat'. Yes I know, it does not make sense (at least not to me).

[hegemon]

That sounds very familiar. I'm sure I've read it, but I can't recall the author or title.

[JP]

That sounds very familiar. I'm sure I've read it, but I can't recall the author or title.

Can you remember any other details about the story?

[hegemon]

I really can't remember any other details. In my mind, the print story is mixed up with a post apocolyptic movie where a young man and woman see a movie poster in an abandoned subway tunnel.