Final Fantasy III Tips

Level 7 summon, Leviathan!
By the time you're able to summon, you'll probably have realised that there's a big fishy thing swimming around on the eastern half of the floating continent.

Guess what? It's a super-awesome hidden summon!

After you get the airship 'invincible' during the later half of the game, it becomes possible to fly over to the lake. Simply exit the airship after crossing the mountains, swim out into the lake with your raft, and move towards the underwater shadow.

You'll enter a large, maze-like dungeon. The monsters should be easy enough to beat if your levels are low-mid 40s. Along the way you'll find some weaponry/magical items. After about four/five floors, you'll finally encounter the boss, Leviathan!

If you made your way to the bottom floor without much difficulty, you should be able to beat him just as easily. I suggest having a healer and a summoner set up to provide support to any attackers you may have (Dragoons/Dark Knights/Ninjas are reccomended).

At any rate, once you've finished it off, you'll be granted the level 7 summon spell, Leviathur! Congratulations! Now go try it out and beat stuff up!