Eldritch sites are found on certain tiles and are invisible until the tile is entered by an unit. Each eldritch site is associated with a particular cult. The first time a unit enters the site, a number of things can happen: the unit can awaken a monster, vanish mysteriously, find strange artefacts that give a gain in culture or science, or be infected with a cult. In the latter case, the player is then given the option to start an eldritch religion based on that cult.
Eldritch sites, discovered or not, will cause the population of nearby cities to gradually convert to that cult.
- Forest: Shub-Niggurath
- Coastal Swamp: Cthulhu
- Ocean: Dagon
- Desert: Nyarlathotep
- Hills: Mi-Go
- Tundra: Elder Things
Cults are a parallel layer to religion. Each population unit may be simultaneously a member of an official religion and of a cult. Cultist activity is outside player control and consists mostly of destruction: loss of money, destruction of buildings, research points, etc. Cultists will also tend to kill members of other religions or cults. If a city becomes entirely of one cult, it first turns into a puppeted city and may eventually break free entirely, becoming cultist-controlled, or joining a civ with a compatible eldritch religion.
Cultists may also slip away and found cultist cities in remote corners of the map. These act much like barbarians, but may also send out missionaries to convert people to their cult.
Inquisitors gain the additional ability to stamp out cults.
Military units created in cities that have cultists have a proportional chance to be "infected" with this cult. This tends to give them a morale bonus, but also has negative consequences: they refuse to attack a city or unit that follows the same cult. Being garrisoned in a city will also cause that city's population to start following the same cult.
The stars are right
Every once in a while, there is a period of about a dozen turns where the stars are right. Cultist activity is greatly increased in this period: people convert more readily and cultist military units have increased morale. Monsters may also spawn.
Powerful units that can be independent agents, under the control of cultists, or even under the control of a civ with an appropriate eldritch religion.
- Young of Shub-Niggurath
When first uncovering an eldritch site, players are sometimes given the option to start worshipping the strange beings there. This either starts a religion immediately if a player hasn't started one yet, or modifies the player's existing religion. Each cult consists of two beliefs: worship and horror. These beliefs are added to the eldritch religion in two new slots.
- Shub-Niggurath: +1 faith from unimproved forest tiles, +10% population growth
- Cthulhu: religion spreads instantly to other Cthulhu worshippers
- Dagon: +2 gold from ocean tiles
- Nyarlathotep: +10% research
- Mi-Go: +1 production from hills
- Elder Things: +2 research from tundra
- Death cult: gain faith each time you raze a city
- Strange experiments: may sacrifice population to gain research points
- Strange artifacts: trade routes rapidly spread cult
- Cannibalism: land units defeating another land unit heal 30 HP
- Cult of the atom: Each nuclear weapon generates +3 faith, using it generates a lot
- Shoggoth servants: May use faith to buy shoggoth units
Eldritch religions are simultaneously religions and cults, so all followers of that religion are also cultists of that flavor.
The survival condition
Optionally, the game can be set so that by the mid-21st century, the stars become Extremely Right. Cultist activity increases rapidly, and monsters spawn continually. In this mode, the last surviving civ is the winner.