The Enclave Campaign Setting is based around a number of settlements in the otherwise ruined city of Enclave.
Enclave was once a great city, dedicated to the so-called New Gods. However, in the Holocaust that resulted from the worship of the New Gods, the population was decimated, and only a few survivors managed to hang on. From those survivors are descended the various races of humanity.
As it currently stands, Enclave has eleven major settlements amongst the ruins. It also has many areas unsafe for human habitation.
Power rests largely in the hands of the priesthood of the Old Gods, along with some few settlement and racial power-brokers.