Stormy Sea

Dungeon where you will fight the legendary pokemon Kyogre. Obtainable by beating the game then you should see medicham near your base he'll say something about Lombre then you go talk to Lombre then talk to Whiscash who will give you dive and the location Stormy Sea.

Trivia

 * Stormy Sea has 40 floors.
 * Unlike all the other legendary pokemon dungeons, Stormy Sea will not have a rest area where you can save before battling the legendary so it makes that much harder.