The djinni Calim governed Calimshan for almost a thousand years before someone challenged his rule. On the shore of the River Agis the great efreeti Memnon proclaimed his sovereignty. Despite border skirmishes, assassination attempts, and unfavorable trade status, Memnon's power grew for three hundred years until all-out war erupted between the Calim Empire and Memnonnar, ushering in the Era of Skyfire.
That war lasted for centuries.
Some of Faerûn's most appalling battles occurred during the Era of Skyfire. Battle accounts ink crumbling tomes with names such as the Blood March, the Fall of Agis, and the Battle of Ruin. Both sides suffered horrendous losses, especially so amongst the thousands of slave-soldiers forced to fight for both sides. Before the elves of Keltormir and their djinn-efreet binding ritual permanently ended the clash, many heroes of the conflict fell to noble and ignoble deaths alike.
More than powerless slaves found themselves caught up in the fighting. Stronger entities, too, who cared nothing for either of the two principles, were forced to choose sides lest they be destroyed by the other.
One of these was known generally as the Astronomer. However, the Astronomer would not choose a side. For that, she was brushed aside, and her home disappeared under what became the Calim Desert. Few histories record even that she existed, let alone the location of her buried home.
Who Was the Astronomer?
Despite being kin to djinn, the Astronomer would have nothing to do with the centuries-long struggle for dominance between Calim and Memnon. A genasi, the Astronomer concerned herself only with her study of a burgeoning planar realm she referred to as the Elemental Tempest.
According to the Astronomer, beneath the world the forces of the Elemental Tempest churn. There, elemental substance and energy crash together in an unending cycle of creation and destruction. Its substance, she claimed, was the very stuff from which the world was crafted, and once the scales of ignorance fell away from the eyes of the supposedly wise, all would recognize her claim as so.
Thus the Astronomer's lone home, far from any other home or village, was a facility dedicated to peering into this realm over which she obsessed. Her large compound could support her, her staff of mage-researchers, her household workers, and the explorers that she briefly dangled into the realm via magically insulated Tempest Cages.
When the ultimatum ("Serve me or perish!") from Calim arrived on the lips of a leering captain of one of Calim's many armies, the Astronomer dropped the envoy, unprotected, through a portal to the very heart of the Elemental Tempest.
In Calimshan, tales speak of a lost reliquary contemporary with the famous djinn Calim. This ancient place, called the Tomb of the Astronomer, remains lost in the midst of the Calim Desert, and some say it contains an ancient secret.
If it can be believed, an antique scroll in the library of Candlekeep explains how explorers once or twice stumbled on the entrance to the Tomb of the Astronomer. A half-sunken, shattered stone face in the sand marks the entrance. The wrinkled frown and cold sneer on this visage seems to recall images of ancient Calim, and indeed, the scroll indicates that after the Astronomer's compound was buried under a sandstorm that lasted ten years and a day, a single graven image of Calim, in all his splendor, was set upon the site as a warning to others not to gainsay the will of the djinni.
Excavation of the Tomb
Excavating the constantly shifting, fluid sand anywhere in the Calim Desert is nearly impossible. A hole fills in nearly as fast as it is dug unless the diggers use physical and magical supports.
And thus, if adventurers come upon the site with the antique scroll from Candlekeep clutched in eager hands, perhaps they will be delighted to find someone has beat them to the site and has already started digging. Then again, perhaps not.
The noted collector Dulmanico of Waterdeep is on location, and for several months he has supervised the work of his team of diggers, excavators, sages, guards, and even a few fellow wizard collectors who contributed to the cost of the expedition.
Thus hopeful adventurers discover a slowly growing pit of terraced shelves gradually stepping down to the lowest point of the deepening pit. Nearly a hundred tents, an equal number of camels, a semipermanent barracks and kitchen, and a camp library have made a once-sterile spot in the middle of nowhere into a miniature village. Arcane and divine magic keep the draft animals, workers, and overseers fed, watered, and safe from the heat.
The guards, who Dulmanico pays in ale and silver, busy themselves dealing with the increasingly frequent attacks coming out of the deep desert. The attackers consist mainly of shambling, mindless zombies whose tissues are more fossil than bone. Dulmanico theorizes that the undead are animated recently from an eon-long slumber rather than being the free-ranging zombies who've walked the desert so long that they've fossilized. He supposes an intelligent agent controls them while lurking somewhere farther out in the desert in a hidden base. Moreover, Dulmanico insists the undead attacks are not, as the superstitious workers in the dig camp mutter, the effects of a curse that strengthens with each foot the excavation descends toward the Tomb's buried entrance.
In fact, Dulmanico believes the attacks are orchestrated by none other than agents of the Twisted Rune, a group of powerful undead spellcasters that meddle with affairs in Calimshan and beyond for power and amusement.
If someone could stop the attacks once and for all, Dulmanico would command his workers to excavate the final few feet to reveal the Tomb's entrance, which both mundane and arcane methods indicate would take only a few days of uninterrupted work.
Newcomers to Dulmanico's dig site find him amenable to sharing the fruits of the excavation if they would make a good faith effort; he asks interested visitors to look into the supposed Twisted Rune base hidden in the desert, eradicate the Twisted Rune agent or agents that probably reside there, and thereby hopefully put an end to undead raids. Only investigation reveals whether any of Dulmanico's series of surmises are accurate.
Inside the Tomb
Once diggers remove the final few feet of sand concealing the Tomb of the Astronomer, a pitted iron surface is revealed. Curved seams suggest a great, eyelike iris that is currently closed. A humanoid palm print in the exact center of the iris begs to be touched. If it is, the eye responds.
A terrible scraping sound accompanies the opening eye. Excess sand around the edges pours into the opening like a liquid flood, but apparently the space beyond the aperture is more than large enough to contain it.
The rusted, newly sand-filled chamber beyond contains no immediate threats, furnishings, or distinguishing furnishings (unless falling sand buried them). The chamber is apparently carved from solid rock. Corridors lead off in several directions, though one corridor is more than twice as wide as all the others, potentially indicating its importance.
Disturbingly, demons have somehow gotten into the Astronomer's buried facility!
Soon after explorers begin to move through the chambers, several demonic creatures attack them. These demons are initially as astonished to discover visitors as visitors may be surprised at encountering them. However, demonic eyes quickly alight with anticipation as they attack.
If the explorers overcome the demons, they soon enough find the main observing dome with its rusted arcane instruments, shattered lenses, and forgotten astronomical scripts. There they can discover that the magic mechanism for opening the dome for observation still functions. If they trigger it, the dome splits, though it doesn't spill sand into dome. Instead, it opens onto a view into a different plane -- perhaps the Elemental Tempest itself!
The view through the opening is of a floor of black stone stretching away in all directions, though the landscape is broken up by rivers of lightning, seas of fire, floating earthbergs, ice mountains, and cyclonic columns of air, fire, and soil.
In the far distance, a fire-rimmed stain of darkness hangs in mid-air, as if a scar on the sky itself. According to notes found half-shredded at the observation stations under the dome, the scar is the physical manifestation of the Abyss within the Elemental Tempest.
Thankfully, despite being visible, the burning scar is hundreds of miles off, but perhaps it explains the demonic infestation of the compound. Certainly the rusted, now-useless instruments in the dome appear as if they may have once been trained on that distant blot.
What was the Astronomer really studying here? What does the view into the obviously very real Elemental Tempest have to do with the Abyss and demons who swarm and breed within it? What other secrets does the demon-infested, observatory-turned-tomb hold? And does any aspect or memory of the Astronomer herself yet walk the hollow stone halls?