Quote Originally Posted by Ultima Cloud View Post
The sunken submarine at the bottom of the ocean. Over there u fight Unkwon 1,2,3, and Serpents in the back hall. If you don't know where this place is I think its where you find the Highwind Limit Break (Cid) and the Summon Hades.
Quote Originally Posted by Mirage View Post
Contrary to popular belief, the sunken plane is not better than Mideel.
Sunken plane enemies are stronger than mideel enemies, but gain you about the same amount of exp and AP. This means leveling in mideel allows you to kill enemies faster, and requires you to heal up less in between fights. Much better exp in the long run.

However, the northern crater itself is definitely the best leveling spot, both for exp and AP. Especially if you like to exploit the W-Item glitch :).