Atlantis
Many scholars think that Plato could mean a real place when he was writing about Atlantis. For example, there was a Minoan kingdom on the island of Santorini.  The Minoan kingdom was very powerful thousands of years before Plato, and their society was damaged when a volcano erupted on their island. According to Plato, Atlantis was very large, as big as North Africa, so it should not have been hard to find.