From back cover:
In R'lyeh, Cthulhu Stirs...
Evil cultists consummate their union with Shub-Niggurath in dark woods no other mortals dare go. Alien terrors lurk in the underworld; their vast riches wait, or their incomprehensible powers could leave you broken, dead, or worse. Adventure in underworlds filled with horrible entities, or the ruins of alien beings that enslaved the ape-like ancestors of mankind. Seek hidden secrets from the arctic wastes to dark, briny seas. But as you approach the ocean, what are those strange longings you feel?
Realms of Crawling Chaos is a Lovecraftian Dark Fantasy campaign supplement for Labyrinth Lord and the Advanced Edition Companion.
In this book you will find:
New player races, including white apes, white ape hybrids, sea blood, and subhumans.
New spells
New monsters
New artifacts and a system for designing unique artifacts
Rules for psionics, compatible with Mutant Future