Five Call of Cthulhu Resources As Fodder For Your Old School Sword and Sorcery Campaigns

“The living close the eyes of the dead,
but it is the dead that open the eyes of the living.”
— Old Slavic saying

Call of Cthulhu is the classic horror rpg and one of the best under used resources for old school sword and sorcery rpgs. Each of the following adventures and resources are perfect fodder for a great old school D&D style campaign. For example Beyond The Mountains of Madness has a metric ton of information on the Elder Things and their machinations, history, and works, as well as time frames that could be used by a DM to incorporate them into a mega campaign. 

From OD&D and their retroclones to AD&D there is room to incorporate much of the Mythos from Chaosuim and their products into your old school horror gaming.
Terror Australis is one old school Call of Cthulhu book that I love to use for for games like Carcosa and much more. The book contains everything I need to run a dream time based campaign along with everything about the Great Race of Yith. In terms of sheer volume many of the backgrounds of the book are simply fluff that can be added to an old school campaign to add a very different lost world style of setting flavor.

You can find all of these books and more on Chaosium's Website right over
HERE

Shadows of Yog- Sothoth is simply one of the best resources for a world spanning cult that I've seen that can be mined for a ton of ideas. Everything from the early beginnings of a cult to time travel then there are the breath taking encounters with the Mythos that can easily added to any Sword and Sorcery adventure.  

Secrets of Japan is one of my all time favorite go books for a very different take on the Mythos. Everything is laid out from the ancient Mythos fused history of a weird Japan to hints of cults that stretch back to the beginning of recorded time. This is a big book that should be taken in bite sized doses for use with your favorite retroclone. Many of the ideas here are easily translated into a sword and sorcery adventure background and drip all the way back to the beginning  of unknowable eras. 

My all time favorite CoC book for use with OD&D and its ilk is Cthulhu Dark Ages. I've used this book time and again as fodder for D&D. The book has a great feel and all of the standard Mythos monsters in one place as well as cosmology of insanity waiting for adventurers to blunder into. 

This book also happens to have one of the most flexible backgrounds to inject monsters from OD&D right into the Dark Ages background. This isn't a heroic setting but a bleak and unforgiving place right out of mythology and legend just waiting for some D&D style adventurers to blunder into. I've actually used the setting to run a very dire version of 'Keep on The Borderland'. None of the players were aware that they were playing an old favorite until the maps came out and the encounters became more intense and more savage.
The Caves of Chaos became whole different ball game when the Mythos influence became evident. A very nasty and dangerous mini campaign resulted. Cthlhu Dark Ages remains one of my all time favorite books for use with OD&D.