On the world of Ranais there was a city called Moil. Moil was built on the surface of its world and it daily saw the light of the sun as every normal city did. The uplifting light of the sun, unfortunately, was not sufficient to keep the citizens from dark pursuits: the Moilians were of an evil bent, and gave their worship to a powerful demon lord they knew as Orcus.
As is the way of such things, the citizens of Moil reaped only a bitter reward for their patronage to this chaotic lord. In the passage of time the Moilians allowed their piety to fail in favor of less bloodthirsty deities from other cultures.
Predictably, Orcus was wroth. In horrible but unlooked-for vengeance, the entity cast what initially seemed a mild curse over Moil: its inhabitants fell into enchanted sleep that could only be broken by the dawning of the sun. Orcus then physically removed the city from its natural site and transformed it into a nightmarish, lightless demiplane of its own, assuring that the sun would never again shine upon its tall towers. Having completed their deed, Orcus dubbed the demiplane anew as The City That Waits.
Over time, the slumbering Moilians all perished in their dark sleep, leaving the place strewn with unquiet dead and dangerous dreams. But Orcus came never again to the city, for he was slain by Kiaransalee, drow goddess of vengeance, and passed from the knowledge of man and god alike.