Sounds cool!
I did a shipwreck/washed-up-on-beach start to a campaign once, and it's a cool challenge for the players. They had to pick through the wreckage to try and put together some equipment: a weapon here, a bit of armor there, a shield, maybe a sack, damp rope, etc.
Do you envision the PCs knowing about Atlantis, or it being totally alien and something they have to uncover answers about?
Larry Niven had a cool concept for Atlantis in a novel called
The Magic Goes Away. Basically, it was only the magic of the priest-kings that kept Atlantis afloat. When the Greeks invaded and slew the priest-kings, the magic died, and then came the water. So much for Atlantis, so much for the Greek invasion fleet.
What do you have planned for Atlantis, and the PCs?
Thanks,
Warrior Poet