Atlantish

One contemporary theory holds that the myth of Atlantis, apparently first written about by Plato in a book that was, shall we say, probably not intended to be a travelogue, was actually based on the city of Helike, located on the coast of Greece about 40 miles West of Corinth.

It seems to be fairly well established that this city existed-- there are coins and other artifacts that still survive.  And it's a matter of record (as much as anything from that era is) that it was destroyed in 373 BC-- about 10-15 years before Plato's writings.  There are surviving reports from the time telling of earthquakes, fleeing animals, and the sudden submersion of the city, practically overnight.  And Plato almost certainly would have heard of the disaster, and he was the type of guy who would incorporate such a thing into a morality tale.  But it was fairly well hidden.  Despite written evidence, it was pretty thoroughly buried in silt, and only rediscovered about 10 years ago.  Excavations are proceeding slowly.

http://www.bioone.org/doi/abs/10.2112/05-0454.1