The physical setting of "God’s Grandeur" is our planet, Earth. Though the poem was written in 1877, the images are easily transferable to today.
In the poem, the earth has a problem. Humans, in their struggle, have been mucking it up, caring more about money than preserving and protecting the planet. In the first stanza we see big factories, smoke stacks, and polluted waters and lands. In short, the first few lines present us with a barely inhabitable planet.
But then the poem moves underground, and shows us nature in hiding, full of potential, waiting to show its face again on the earth’s surface.
After that the setting is all sky – sunrise, sunset, the cloudlike image of the Holy Ghost as a dove, hovering over the planet.