City Under the Stars by Gardner Dozois

God was in his Heaven—which was fifteen miles away, due east.

Far in Earth’s future, in a post-utopian hell-hole, Hanson works ten solid back-breaking hours a day, shoveling endless mountains of coal, within sight of the iridescent wall that separates what’s left of humanity from their gods.

One day, after a tragedy of his own making, Hanson leaves York, not knowing what he will do, or how he will survive in the wilderness without work. He finds himself drawn to the wall, to the elusive promise of God. And when the impossible happens, he steps through, into the city beyond.

The impossible was only the beginning.