I haven't actually EXPLORED this place "physically" yet, but I have a thing for gathering information...so here goes. You do a quest to gain entrance to the teleportation device in Hall of the Gods, first off...and port to Ru'Aun. Judging by maps and about 5 million posts I've read, this area connects to Ve'Lugannon Palace, Shrine of the Ru'Avitau, and possibly La'Loff Amphitheater and the Celestial Nexus...not sure on the last two, almost nobody talks about them. All the NMs here have an ultimate purpose: to grant access to a battle with Kirin (Japanese for God, apparently...strange, he was just a weird horse with a group regen in ff6). First, there's 8 NMs you're supposed to kill:
Ru'Aun:
Despot (drops Gem of the West)
Ve'Lugannon:
Brigandish Blade (Gem of the South)
Steam Cleaner (Gem of the East)
Zipacna (Gem of the North)
Ru'Avitau:
Faust (drops Summerstone)
Mother Globe + 6 Slave Globes (Springstone)
Olla Pequena/Media/Grande (Winterstone)
Ullikummi (Autumnstone)
Then, there's 4 more NMs that each require a combination of 1 specific gem and stone to battle; these 4 are sort of sub-gods under Kirin (and anyone who's played Seiken Densetsu 3 may recognize them as parts of the names of the special attacks of the final 4 forms of the werewolf)
Genbu (North, Winter)
Byakko (West, Autumn)
Suzaku (South, Summer)
Seiryu (East, Spring)
Each of those 4 drop a seal named after them...when you have all 4, you can summon up Kirin to battle. I would -guess- that Kirin's the toughest mob in the game, though I've heard horror stories about the King Behemoth and Fafnir...and then recently hearing about the lottery pop, Nidhogg, with Fafnir makes me wonder even more (come on...a lottery pop with an already-incredibly-powerful NM?). Also, I've found virtually zero info on any Dynamis mobs thus far. Well, guess I'll have to get an alliance or 3 and kill them all to find out...heh.