After reading the question, I initially decided it should be capitalized, like, say, the Aleutian Islands. Multiple places are still places. However, after reading the responses, I'm fully convinced lowercase is correct.
I think, though, that it may depend on the POV and genre. If it's contemporary fantasy and omniscent, maybe caps are correct, but in another world/time/culture with POV character familiar with the term, lowercase fits the bill.