It's hard to say where this poem takes place geographically. It probably has more to do with a dreamland, or that subconscious place where poems come from. We don't get any concrete references to a real place, but there are some wild deserts and seas. Plato's famous cave is an imaginary place that is referenced in line 10, but it's an important one in the cultural landscape of Western civilization.
There are also some references to places that don't exist anymore, but did in ancient times, like Epicurus' and Netzahualcoyotl's gardens. This puts the poem smack into a long, classical tradition—Paz is no dummy! He knows how to situate himself. And above all else, in terms of setting, he situates this poem in the realm of the possible. As the lines sketch out all manner of metaphors for exploring the possibilities of poetry, we can best think of the backdrop to these lines of inquiry as a little place called… Imagination-land.