Atlantis was an island located about where the islands of Thera and Santorini are now. It was a typical bronze age civilization that preceded the Minoans. The ancient Greeks and Egyptians had heard about it in legend. It was destroyed in a volcanic explosion that left an underwater caldera and smaller islands around the rim of the caldera. They left two writing systems, one of which resembles early Greek, while the one they used most has not been deciphered. They may have spoken a non-Greek language.
The scribe who wrote about it mixed up his number multiplier, like putting the decimal point in the wrong place. So the location and date are off by a factor of about 10. Yes, it really was in the Mediterranean in the bronze age.
It's exciting for people who are into archaeology and linguistics, but too mundane for fabulists and those imagining early utopias.