The City of Eternal Twilight
Traveling east, the party unexpectedly encounters desert. The Ranger and Druid recognize this as somehow unnatural, though there is no magic involved. After a few more miles, the source becomes evident: a deep trench is cut into the ground, draining the local water table. The trench stretches east for as far as the eye can see; at its mouth is a construction crew busily extending it further west.
The crew consists of men wrapped in white against the desert sun, two large self-propelled animated cranes, and a massive stone golem. When the party cautiously approaches, one of the men rushes out to block them, holding a staff ending in a flat hexagonal plate, and shoos them a safe distance away from the ongoing construction. At this range they realize the man is dead and mummified.
Uncharacteristically, the party decides not to start a fight. Instead, they follow the trench east. The water gradually gets deeper and faster as the land slopes down; the artifical drought around them becomes older and older, revealing that the crew has been working for several hundred years. Eventually the canal flows into a gigantic bronze portcullis, set into a high wall surrounding a massive city several miles wide. From the height of the slope they can see at least two interior rings of walls, implying the city has been built up for centuries.
But as they approach the city, it becomes clear it is virtually uninhabited. They evade a patrol of mummys and scale the wall at a deserted spot. On the other side are huge stone buildings, some six stories tall, that should be apartments or shops or theaters but are instead simply empty stone structures. Nothing travels the streets, save for the rare patrol of mummified minotaurs in blue hats, or even rarer, a construction crew building even more unused buildings. Inside some of the apartments are stacks of corpses of indefinite age, both human and minotaur.
At the center of the city lies a pyramid, clearly the source of answers to this mystery. Even more appealing: on top of the pyramid is a glowing light so bright that even when the sun goes down the city is bathed in twilight. This must be the recently fabled Disk of the New Sun.
Upon approaching the pyramid, the party is intercepted by a patrol that seems to be looking for them. They allow the patrol to shepherd them into the pyramid, through its winding corridors, and into the presence of the ruler of the city: the mad, mummified priest of Kek.
This high-ranking priest has been dead so long that he appears to think he is Kek, God of Twilight. The party accepts his self-identity, since they are after all models of polite behavior. Kek is not at all unfriendly, despite being somewhat unhinged, and appears to enjoy talking to people who are not silent robotic construction machines. Kek very quickly gives away all his secrets: the giant pool underneath his pyramid that all four trenches (east, west, north, and south) drain into, the portal that transports the water directly to the surface of the sun, and his epic quest to dump enough water on the fire of the sun that it is modulated to permanent twilight instead of harsh daylight and deep nighttime.
The party does not actually know how the sun works, so they are not prepared to dispute his calculations. Instead, they ask if they could borrow his night-light for a bit so as to deal with some vampires.
Kek has a low opinion of vampires in general and the Kingdom of Night in particular, so he is amenable. However, according the Law of Balance, the party must do something for him in exchange. He suggests that the annual tribute of tael from one of his minor client states to the south has been subject to depredation by a nest of Nagas. If the party could exterminate his problem, then he could lend them the means to exterminate their problem. This seems like a good deal, apart from the part where Kek seems largely unable to distinguish between lengths of time like hours, days, and years.
The party joins the procession south, which is essentially just another construction gang. Along the way they are indeed attacked by Naga bandits who remarkably have the ability to neutralize the stone golem by enclosing it in a force cage. This works equally well against the Barbarian, much to his dismay, but the party defeats the bandits and easily catches back up to the caravan.
Eventually they arrive at a small primitive human kingdom and witness the tribute. The village's dead for the year are reverently loaded onto the wagons, to be transported to the Eternal City where they will be reanimated and live in luxury according to their good deeds in this village. The party, remembering the stacks of dusty corpses, chooses to keep quiet, as little good can come from destroying the villager's hopes, and after all, Kek is not particularly oppressing them, taking only the usual overlord's tax of tael.
The villagers are well aware of the Nagas, and even trade with them, so it is easy to obtain a guide to the nest. Once there, the party has little difficulty extirpating the nest, despite their force cages, unusual cold spells, and charmed minotaur guards.
Returning to Kek, they hold him to his bargain, and obtain the Disk of the New Sun for the next one hundred days. Now they march west again, determined to destroy the immediate threat of Morpheus and his plans to return to the world. Foiling the mad Kek's quest to drain the sea and turn all the land into desert and the sun into twilight will have to wait; fortunately, that threat will require another thousand years to be really dangerous.