Concerning "On First Looking Into Chapman's Homer," by Keats, you probably need to look elsewhere for your medieval settings. And while the lines you quote refer to exotic locations, the poem itself is not set in an exotic locale.
The passages that present the speaker's previous travels contain allusion--to the Greek god, Apollo, the god of music, poetry, and medicine--but in general these lines merely create a contrast between the vast traveling the speaker claims to have done and the real discovery he felt when he first read Homer. They are not in themselves central to the poem or specific in nature. What is central in the poem is the speaker's discovery.
The enotes Study Guide on the poem says the following:
The focus throughout the poem is on the feelings engendered in a person when a discovery is made. The narrator expresses himself directly to the reader, attempting to find parallels to explain what it feels like to make a great discovery for oneself. To make that feeling clear, the narrator speaks of himself as a traveler who has set out to explore uncharted lands—at least, uncharted by him. He portrays himself as someone experienced in visiting exotic places (“realms of gold,” in line 1) and as having seen “many goodly states and kingdoms” (line 2) among the “western islands” (line 3) that are inhabited by “bards” who pay homage to the god “Apollo” (line 4). The conscious reference to poets and to the Greek patron of poetry should suggest to readers that this is not a literal journey; instead, it is intended to represent the mental travel one undergoes when one enters the imaginative world of literature.
So if all you need is mention of exotic places, you're all set. But if you need a poem set in an exotic place, then this poem probably isn't what you need.
Finally, yes to the symbolism part of your question. According to enotes, the exotic locale is symbolic of the exotic and imaginative world of literature.