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Carcosa: Realm of Hastur, The King in Yellow

Origin and History

Located on an unnamed planet in the Hyades star cluster, Carcosa is the domain of Hastur, the Great Old One. This malevolent entity, often referred to as The King in Yellow, is believed to be confined within Laååke Hali, a vast body of water on this celestial body.

Once, this unnamed planet was home to two main civilizations - Alar, an aggressive and rebellious society, and Yhtill, a city of artisans and aristocrats, known for its stagnation and decadence. Carcosa was the third metropolis, an abandoned city-state that predates the mud-and-stick settlements of Alar and Yhtill. It's said that Carcosa would appear across Lake Hali during the black sunsets, fostering many legends, with some suggesting it was Hastur's home before his imprisonment.

Transformation of Carcosa

Hastur, not content with confinement, devised a strategy for his liberation. He manipulated the people of Alar and Yhtill to facilitate the conversion of Carcosa into a tool for his release and subsequent apotheosis into an Outer God. Hastur mystically united the three cities, causing Alar and Yhtill to be absorbed into Carcosa, thereby reanimating its dormant structures.

In this transformation, Alar contributed its aggressive spirit, while Yhtill lent the new Carcosa its power of corruption. In the process, however, a fragment of Yhtill's vitality found a host in Queen Cassilda, making her a lesser immortal and the first inhabitant of the reformed Carcosa.

Living Entity and Parasitic Function

Carcosa transcends the ordinary definition of a city. It is a living, alien entity that can establish mystical connections to distant civilizations and drain their cultural life force. Through this process, Carcosa grows, assimilating a twisted replica of the consumed city into itself, which is referred to as a nexus. This predatory action ultimately leads to the entire city and its inhabitants being transported to Carcosa.

Furthermore, Carcosa can establish these connections through complex rituals often embedded in performance arts like plays. An example of such a ritual is hidden within the theatrical play "The King in Yellow," which can incite madness among viewers or even transport them directly to Carcosa.

Inhabitants and External Influences

Carcosa is inhabited by monstrous creatures, including the flying polyps that serve Hastur after one of their cities was devoured by Carcosa. Additionally, the Great Old One Xhamen-Dor, an infestation within Carcosa's sewers, aids in the city's growth by corrupting planets and siphoning psychic energy back to Carcosa.

Carcosa currently contains nexuses of over 100 cities, but only three cities are known as of this date - Aevan-Vhor, an ancient Azlanti city; Bohlvarai, the ruins of a city where shoggoth slaves rebelled; and a section of Paris from Earth, taken during a mishap involving the performance of "The King in Yellow."

Physical Properties

Carcosa exists on the Material Plane, in a far-off cosmic location from Golarion. Its environment, although heavily influenced by magic, maintains comparable gravity to Molderia. Carcosa is also characterized by its twin black suns that emit pale, yellow light and its ever-changing city layout as new nexuses are absorbed.

The city is also unique in its invisibility to those who are unaware of its exact location, and its name becomes automatically known to anyone who either enters it or sees its image. Furthermore, parts of Carcosa can always be seen across or upon Lake Hali, similar to a mirage.