Each entry begins with an overview of the castle's history, the events and decisions that led to its construction, location, and what occurred to set-up its current circumstances. These sections lend character to the halls and parapets of each location. The entries next include a description with an accompanying map and key to expand upon what may be found around each individual location. In case you don't know the difference between a bailey and a battlement, don't worry; the book includes a useful guide to castle terminology. Next up are the denizens, the most prominent characters at a particular location. This includes not only pertinent leadership like the current ruler or captain of the guard, but a grizzled blacksmith or traitor in the midst to be found at a site. The threats section provides an overview of the trouble an enterprising adventuring party is likely to run into. Each castle is set for a different level of adventurers and gives levels or Monster Manual page numbers to help create or locate enemies quicker. Each threats section includes at least one fully stated NPC. Finally, though already filled with hooks and opportunities, each castle includes a miniature adventure, expanding upon the already detailed map and providing a particular challenge for PCs, including some suggestions for hooks on how to bring a party to the location in question.
Castle Everstand: Right off the bat, Castles of the Inner Sea proves that it's not going to be a collection of stale locations. Castle Everstand is an important fortress holding back several orc hordes, but what stands out about it is that it was created from a deck of many things. The history section for Everstand is the highlight, telling the waning tale of the war and the circumstances that led to the fantastic castle's creation and the subsequent expansion to turn it from a magically constructed keep into a true castle. Castle Everstand is relatively safe and a good location for a low-level party to adventure around or to serve as the base of operations for a higher level group.
Castle Kronquist: This is a place where only bad things happen. Castle Kronquist is a dark citadel now overrun by vampires and other undead. Everything about this location exudes evil and is the sort of challenge where only high-level characters need apply themselves. The highlight for Castle Kronquist is the adventure “Crypt of Cvotgar” which tells the story of a vampire hunter who was captured, turned into a vampire himself, and then experimented on by the castle's resident “doctor.” Now part Frankenstein's monster, part vampire, part crazed, revenge-driven maniac, Cvotgar poses a real threat both physically and politically to the castle's true master, and Cvotgar's section of Castle Kronquist is a challenging and tricky dungeon that would make for a fun crawl.
Citadel Vraid: Hellknights. Why'd it have to be Hellknights. The infamous order from Cheliax have a stronghold in Citadel Vraid; at least the Order of the Nail does. Citadel Vraid is a complex fortress built onto a mountainside. The map for this citadel is crazy, sprawling across several peaks. Citadel Vraid is in many ways the most vanilla of the castles in this book and this one most seeped in Golarion specific history, but it's a solid entry nonetheless. Also, their Mistress of Blades is a centaur with a great set of stats and a beautiful accompanying picture that shows you don't have to be undead or a clawed and fanged monster to be scary and deadly.
Highhelm: Dwarves are famed for their underground fortresses, but Highhelm has a bit of a twist, as it's built on top of a mountain. Highhelm is easily the largest castle of the batch. Unfortunately, this means a zoomed-out map and a lack of details for this location that otherwise exudes dwarven charm. Highhelm's complex attitudes towards foreigners and politics and merchant laws provide a bounty of urban adventure hooks for a GM and the mini-adventure, Deepscar Keep, is a bonus castle onto itself. Deepscar Keep is fully detailed with plenty of room to set adventures far after it's been cleared of the dangers that initially inhabit it.
Icerift Castle: Building a castle far away from civilization in the middle of the frozen wastes is a bad idea. Just ask those who worked on Icerift Castle. Some of their fellows were driven mad, fighting and eating other soldiers, ignorant to their wounds, but after being abandoned for years, Icerift Castle has a new lord and master, Ugmitok of the wikkawaks. Icerift Castle has a great mystery to it and plenty of dangerous traps, magic, and denizens to make it an ideal spot for an adventure. Also, polar bear mounts!
Skyborne Keep: Two words: flying castle. Skyborne Keep is a castle built by cloud giants to fly around the world. Seriously. Skyborne Keep is hands down my favorite entry, because every piece works so well together. The history talks about early rumors and its rediscovery and subsequent theft by the storm giant Lona Orames. Lona's story is a good one as she works to bring several groups of giants and other beings under her control. Under her rule, Skyborne Keep flies from location to location, pillaging and stealing rare artifacts for Lona's use. It's a giant, flying pirate castle actually flown by giants! As if that wasn't enough, Skyborne Keep is filled with dangerous traps and denizens to make conquering the sky fortress difficult, and each room is fascinating as they cover both the giants' height-specific needs and the workings of a flying castle.
I also have to give a shout out to Castles of the Inner Sea's inclusion of a ton of great women characters, from the villainous Ugmitok of Icerift Castle and Dr. Aryne Ornislovna of Castle Kronquist to the veteran blacksmith Uskara Olym of Castle Everstand and Citadel Virad's mistress of blades I mentioned earlier. That's not all! There is plenty of same-sex love to be had in the Inner Sea as there are references to the leadership of Castle Everstand once including Kelle Gauntwood and her wife Derrin and even the villainous storm giant Lona Orames beds another woman. Thanks for being so inclusive!