Re-Map the World
Let's just assume the water rose.
If you look at a current map of the world you can see that we've built towns and cities near almost every sheltered harbor and river delta. This seems to be part of our nature as a species. That being the case, it would be interesting to use some of the underwater megaliths that have been discovered as markers showing historical sea levels, redraw the world map based on those sea levels, and then send submersibles searching for ruins where harbors and river deltas used to be. This makes more sense than assuming every underwater megalith is the fabled sunken city of Atlantis.