The temple Carl must reach in a Club Vanquisher to petition for permission to break the gods' truce.
The Temple of Issitoq is the destination named in Emberus's quest update, delivered to Carl during The Ceasefire. To learn who killed his son without igniting a war between gods and demons, Emberus instructs Carl to proceed to the Temple of Issitoq in a Club Vanquisher and treat with the High Cleric of the Watch there, gaining permission for the god to break his truce with the demons of Sheol.
Carl has no damn clue what any of it means and pushes it aside as a tomorrow problem, with the Faction Wars and his own team's defenses taking priority.
The seat of the High Cleric of the Watch, and Carl's next quest destination.