There are two major settings in "Eldorado": dark places and bright places—sunshine and shadow, in the poem's words. Well that sounds simple enough doesn't it? Eldorado itself is our big representative of the first setting; the word is used, after all, in the last line of every single stanza in the poem. Yes, all of them. The word itself means "the golden one," and it makes us think of a city where every last thing is made of gold. Gold streets, gold houses, gold dishes, gold toilets, gold… you get the idea. If this sounds a little ridiculous, that's because it is! Gold toilets?! That's ludicrous. But it's supposed to be. Eldorado is a very alluring place, but it's also mythical. It is more fantasy than reality, more shadow than substance.
Speaking of shadows, those guys are everywhere in this poem. It's almost like the speaker can't mention Eldorado without simultaneously talking about dark, scary places as well. The knight travels through sunshine and shadow (3), a shadow falls over his heart when he can't find anything resembling Eldorado, then he meets a shadow, who tells him about these scary mountains and this dark valley that can only be about death. Now, even though there's no specific description of just exactly where the knight and the shadow have their little coffee talk, consider this: can you think of any movie or story where somebody meets a ghost in a bright, shiny place? Nah, it's usually some dark and scary place. In the shadows!
The interplay between these two types of places partly expresses Poe's feelings about the California Gold Rush in the 1840s. The discovery of gold in California gripped the entire nation and, like the knight in the poem, a whole lot of people went in search of what they thought would bring them riches beyond compare. Some 80,000 folks went to the Golden State in 1849 alone.
Like the knight in the poem, however, most people never found anything resembling Eldorado. A whole lot of people went broke after they packed up and headed west. Now, going broke isn't as bad as dying in the middle of the nowhere like the knight, but it sure isn't a good thing. Poe died in 1849 and couldn't have known that a lot of people would suffer in their attempts to find Eldorado, but his poem is an uncanny prediction of what did, indeed, happen. To put that in terms of the setting in this poem: the shadowy, dark reality wins out over the sunny, gleaming, mythical fantasy.