The land of Geb is an impressively creative work of fantasy: an entire empire based on Necromancy ruled by a ghost king (Geb) and an undead Queen. Geb's aristrocacy are mostly all undead.
I say 'mostly' because there are still some living people in Geb which makes the place even crazier - how can one live among such undead? Surely those living people have been seriously warped?
Here's another interesting thing about this place: since everybody is undead, no one eats, but Geb uses zombies to grow food for export. I don't know which is more surprising: zombies growing food or other Golarion cities actually willing to import and eat food grown by the undead.
Anyway, this necromatic empire is a fantastic adventure setting.
I love winter settings and Irrisen is a land permanently locked in an arcane winter.
Even better, it is a Witch Empire founded by Baba Yaga. That name is, of course, a name famous in Russian folklore. I love that the famous witch living in a house with chicken legs and eating children has been 'conscripted' by Pathfinder to become a formidable witch queen, the founder of Irrisen. She no longer rules Irresen though, her daughters do.
Get into this snowy land and have an awesome campaign.
The war between the necromancer Geb and the wizard Nex created the Mana Wastes.
First of all, there are reportedly huge monsters wandering in this area. Second, this area is a lawless no-man's land. Third, magic behaves erratically here. What this all means is that you can have the wildest adventures and discover incredible treasure in the Mana Wastes. Another thing you can encounter from the aforementioned magic war is some animated machinery that is still working ((most likely created by Nex).
Varisia's attraction lies in the fact that it is built on the old pre-Earthfall sorcerous empire of Thassilon. What does this mean? Old, powerful magic, lost temples, tombs, objects, grimoires - let your imagination run free.
Varisia is a place were there is a lot of mystery and possibility because Thassilon used to be a place of powerful and corrupt magicians - a place ruled by the legendary Runelords. This place is bursting with adventurous potential - so many campaigns can be had this location as a destination.
Perhaps the most famous arcane location of all. No less than the gate into hell has been somwhat controlled. Enough to have adventures that don't degrade (improve?) into an actual war against the demons.
And yup, Worldwound = demons, so if you're in the market for an encounter with infernal and abyssal creatures head over to the Worldwound and go beyond the wardstones. Don't say I didn't warn you.
If you're a high-level PC party weilding some serious Arcane or Divine magic (or maybe just a death wish) and you want to test just how powerful you and your allies really are when compared to some serious opposition, these places could be the ultimate playground (graveyard?) for you!