???

Try the north crater i do there

Yep, northern crater is the best place to train if your a high level.
IF your not that high a level you can get quite good AP from the 3 caterpiller things you fight outside Mideel.

yea northen crater but try the sunken sub there are hard monsters there and good materia

Do the W-Item trick and fight the Magic Pots in Northern Crater. Plenty of EXP and AP.

under water sub is the best place with yuffies last weapon and 4x cut+ slash all so easy good experience plus ap

In the beginning of the game, I also like to level up around Wutai area. You'll also get good items around there.

Another good place it the sunken airplane (underwater sub). You'll also get good items there, and you can steal some good stuff from the monsters there.

Or Mideel will be ok, too. All these places are not just good for leveling up, also for using your limits a lot, which means, good for getting the next one easier.

But of course, the best place is the northern crater..... :)

northern crater and mayb wutai

deff northern crater since its near the end of the game-harder monsters to kill more AP

Yeah, North Crater is easily the best place to level up. However, I first went to Mideel to prepare in terms of levels and such. When you enter the pond area in North Cave(if you follow the left path, i believe), you need to do the w-item trick, which then allows you to slay magic pots successfully after givng them each an elixir. They give 8000 exp and 1000 ap each (if you give them each an elixir you produced by process of w-item trick). Movers (red boucing balls), which almost always are in groups of 3, are the best source of ap in the game as far as i know, and give 0 exp and 2400 ap in total. A cool thing to do is to equip exp. plus to your party and your party will eventually be able to gain double experience, allowing your characters to earn 16,000 exp or 32,000 exp each battle, depending on if you fight one or two. Along with that, equipping someone with a triple ap weapon (apocalypse, buntline, etc.) will allow you to gain 7200 ap from movers. This is especially helpful for leveling up really powerful materia (i.e. KOTR, W-Item, W-Summon, etc.) I apologize if most already know this: it probably wasn't needed, but I just wanted to help out those with the same question who didn't know.