The Empty City is the Fear of Disorientation, of being lost and alone. It appears as a sentient city devoid of any life that continuously shifts its shape and structure to keep victims lost forever. Once it has grown tired of playing with its prey, the Empty City will allow them to die and "consume" what's left. It is a domain unto itself and can be entered through one of its many randomly-spawning Doors.
Some habe hypothisized that The Nightlanders are former victims of the Empty City that escaped as shadows of their former selves. Outside of this possibility, the Empty City has no servants.