Title : Occult Realms
Publisher : Paizo Publishing
Occult Realms is an expansion to the Occult Adventures. It's a little on the smaller side as far as supplement books go, only clocking in at 63 pages. However, the book does have some useful and frankly quite delightful offerings that make the $20.00 I paid for it worth it.
While I run all my games out of my long running homebrew setting, those who set their adventures in the Inner Sea area will find a lot of location specific lore in this tiny tome.
For me the biggest standout is the occult location chapter that covers both small and large areas from the Vergan Forest in Razmiran with its haunting Bleachbone Cave, to The Center for Psycogenic Advancement tucked away in the city of Promise. Even if you are not running in the Inner Sea area the ideas that are conjured up in this little book are really worth a look if your storytelling leans more towards the mystical and occult side of things.
However, the locations are not the only thing this book has to offer. It goes into optional rules for each of the Pathfinder occult classes, new rituals that allow the PCs to attempt to attain lichdom, and rules for creating idols that gain power as a cult that follows them grows in influence and power.
From the storytelling side of the screen the idol creation is a really nice avenue to inject some followers, priests, or cultists who are new to the game you are running. This works particularly well in some cases where you have an established pantheon and do not want to introduce a new "god or goddess".
Sometimes you need a particular brand of zealot that does not upset the overarching world building you have going on and I think these idol rules really step in and fill this need. It also works really well when you want the "party fighting a god" moment but you do not want them to fight an actual god. Sending them on an adventure through a few temples and hidden locations where cults are gathering to eventually come upon the idol itself, and perhaps a manifestation of the entity that is powerful, but not as powerful as, say, a god, or even a demigod.
All in all I think this is a useful tool for Storytellers and has some fun art, but unless you are really into collecting the books you can pass on it if you want.
Ask your local bookstore if they have a copy or you can pick up the softcover or snag the PDF from Paizo.com