Nameless Cults

Unaussprechlichen Kulten, by Friedrich Wilhelm von Junzt (1839; German)

A travelogue of the horrific, providing ample details of many Mythos cults, conspiracies, and activities. Skimming this book (four hours) provides 1 dedicated pool point for any Investigative ability involving cults, usable once during the adventure. (The Keeper chooses which ability, and may or may not tell the player.) Poring over it (reading between adventures) adds +2 to your Cthulhu Mythos rating.