Lovecraftian setting, the fictional homeworld of the Great Old One Hastur. The setting is reminiscent of various Dying Earth fantasy genre games (such as Dark Sun).
Carcosa is enhabited by various warlord-ruled city states who use cruel magic and human sacrifice to appease the Cthulhu Mythos beings that threaten them. The world outside the cities is bleak and unforgiving, full of deadly monsters and bandits with little in the way of natural resources. There is a high level of technology in the game in addition to magic, but much of it is alien, created by the mi-go and other races, and operates according to principles that can induce madness. Various human races inhabit the planet with skin colors often in bright primary colors (such as blue or red), or even in colors that don't exist in the normal spectrum of light (the colors Jale, Ulfire and Dolm).