In my current game, the PCs have made an enemy of the Red Mantis and will no doubt in the future plan an attack on them. This is great but also terrifying to me as there is nothing in print on this. So I turn to the Community here to get guidance and perhaps develop something for temporary use until Paizo wows us with their own version.
I recently asked James Jacobs to describe the Crimson Citadel and he stated that he considers it to be a "Citadel sitting on top of a Megadungeon". It's the "Megadungeon" part that is kind of overwhelming to me as these usually entail several hundred pages of material (more than one person could conceivably come up with at any rate). Anyways without further ado, let's get started.
Known factors of the Crimson Citadel -
According to Pathfinder #9 there are 4 main parts. The first part is the Ruvaria or the Ruby Halls. In this area there are all sorts of poisoned razors and traps as well as poisonous beasts running around to test the mettle of the initiates. The second part is the Sivlamik or the Honeyed Gardens. This area is filled with pleasure groves and bubbling blood fountains. It is inhabited with "guardian slaves" who are essentially prisoners. The third part is the Odalis or the Lavish Heart. This area has the living quarters of the upper ranking Red Mantis, meeting halls, workshops, and treasuries. The last part is the Faynas or the Iron Heart. Here is where the Blood Mistress resides, where the Red Mantis keeps their greatest treasures and weapons and where the Sarzanri Library is.
According to James Jacobs the Sarzanri Library is so expansive that it should encompass about 3 levels worth of encounters (stated between 14 to 17 or the equivalent to an entire volume of an AP). Which means that the library itself is likely several levels of the Megadungeon on it's own.
I'm sure there are more things but I'll add them later after I conduct more research.