I see goofy stuff in support of Atlantis or other prehistoric civilizations that might be underwater today, but nothing which even rises to the "hmmmm" level for me.
The lone exception to that is the theory about the Black Sea suddenly becoming inundated from the Mediterranean at some point, wiping out coastal communities and serving as the source of the legend of Gilgamesh and Noah's Flood. But the archeological evidence hasn't been found yet to truly support it.
The old shoreline more than 500ft underwater has been found as well as structures around the shoreline. (Ballard)