"Dream-Land" is mostly about sadness and spirits, but, at the same time, Poe sure spends a lot of time talking about the landscape. In a sense, it's kind of like a twisted nature poem. The whole middle part of the poem reads like a (really trippy) travel guide. We get a kind of tour of the natural sights in "Dream-Land": "And, on your left, you'll see the ocean exploding into the sky, which is on fire." OK, maybe this is weirder than a guidebook, but it's still all about how the natural world looks, and how it makes us feel, or maybe reflects our feelings.
Poe creates a landscape that exactly matches both the pain and the loneliness that the speaker feels. In the speaker's dream, the natural world becomes a mirror for his mental state.
Despite the intensity of the descriptive language in this poem, the specific features of the natural world remain vague. This amplifies the dream-like, intangible quality of the world Poe describes.