In the 80's I snorkeled off a friend's property in Crete, a cliffside with stairs cut into the rock down to the water. In other areas, there were abandoned stairs....with 25-30 under the water. At least that is as far down as I cared to check. He said there were places where one could find 85-90 down, but needing tanks to do so.
Water levels have been rising a lot longer than anyone has thought, or else several people hundreds of years ago devoted their lives to a joke nobody ever caught onto.