I am going to leave here to vote for Atlantis
As for why it is so popular, I think part is the mythological aspect, did it exist, was it really before Christ, were they that advanced, did they sink into the ocean, and was it due to natural or other causes?
For me, also another reason is I love to read paranormal romances, one of my favorites is about a race of immortals who are survivors from Atlantis. They had nanobio technology where they put nanos in the boby to repair injuries. Didn't know they would keep on repairing and needed blood to replicate; were given blood transfusions.
Atlantis sank (B.C.) and nanos gave them fangs and other abilities to survive. Present day they drink bagged blood and series focus is mainly on one family, and hunters of rogue vamps and of course falling in love and finding a life mate. Humorous writing.
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Adding so far the results are:
Atlantis 22%
Asia 24%
India 6%
Art Deco 32%
Farming 14%
If not Atlantis then Asia would be my next choice. Sorry, I just don't see it, what is so great about the Art Deco?