"It's a myth, nothing more."
--Noted Human Scholar, Dennal Brown
...on the Elemental Plane of Air, Ennessa Hauri, the half-air elemental king, invited a waundering magician into his kingdom. After entertaining him, the king took the magician aside and asked him to build a palace fit to serve as a symbol for all of Hauri, describing magnificent floating palace of impressive size and design with walls of liquid crystal and ivory, millions of spires bending the winds to produce music and rings of protective gales surrounding the intricate structure. The king saved most important detail for last. He explained that the palace must have at its heart a cathedral devoted to Aerin'al, the goddess of the skies; one to shame any other in all creation. "As I cannot imagine such a thing," the king advised, "I leave the work to your capable mind."
Intrigued, the magician agreed to the work and again set off on his travels. He studied the architecture of the dwarves, the glasswork of the City of Brass, the tumult of the Elemental Storm and temples of every creed and religion. He wandered for years, compiling books of information on the necessary measurements, materials, enchantments, protections, designs, et cetera while gathering an army of architects, arcanists, engineers and construction specialists of all varieties. Finally, eleven years after accepting Hauri's offer, he set to work.
The construction took more than fifty years to complete. When it was finished, the king surveyed the palace and found every detail to his liking. The magician, exhausted from his endeavor, asked the king for one favor: that he be laid to rest inside the cathedral that he had devoted much of his life to build. Hauri gave this much thought but ultimately decided against it, believing it would defile the temple's sanctity. He tried to negotiate with the magician, offering him a place in the royal vault or the catacombs reserved for legendary warriors, but the magician was adamant. Within the year, the magician was dead and the two had still not come to an agreement. The king laid the body to rest in the catacombs, believing it to be the best course. The king passed away years later, believing that he had given his kingdom the greatest treasure in the multiverse.
On the sixty-first anniversary of the magician's death, immense clouds gathered around the palace. Hundreds of thousands of the meticulous spires shattered in unison, causing a splintered note to reverberate through the kingdom as inexplicable gales and lightning strikes laid siege to the palace. By midday, it lay in near ruins.
Recovery work took weeks to restore the palace to a functioning order. Among the many noted structural changes, the most obvious was that the center of the palace now a housed a ruined hall--one that no one could remember a single thing about. Indeed, all memory of the Cathedral disappeared with the storm.
No one among the king's court could divine any information about the storm or the palace's heart. While some servants almost remembered events of something both grand and horrible; and others had nightmares of terrible gales, beautiful cathedrals and vengeance demons, their concerns were dismissed as further effects of the storm. Over the years, the palace was restored to a fraction of its former glory and the ruined hall, considered an undesired monument by many, was cordoned off and hasn't been acknowledged since.
The storm that took the Cathedral from the Plane of Air was conjured by the Magician who built it. Angered that his last request in life was ignored, his restless spirit lingered in the catacombs, plotting to reclaim his masterwork from the Hauri lineage. After many years of scheming and dealing with extraplanar entities, he completed his plan to move the Cathedral to the Material Plane and hiding it in the unreachable depths, an added precaution against the Aurans.
Not satisfied with just stealing the Cathedral, the Magician decided to completely wipe it from Auran and Hauri history. No matter how he tried, he could not conceive of a plausible way to wipe the memories of an entire nation. Frustrated but unrelenting, he forced himself to barter with Olidamarra. The deal he offered was that the god would take the memories of the Hauri Kingdom in exchange for having the hidden temple rededicated in the Trickster's name. Intrigued by the devilish ploy, Olidamarra agreed and when the Magician attacked the palace, the Laughing God wiped the memories of the Cathedral from every Auran mind. Ever the trickster though, Olidimarra immediately turned on the Magician, going to Aerin'al in the guise of Obad-Hai and revealing the plot to her along with the Cathedral and its creator's current location.
Angered by this news, she appeared at the temple unknowingly followed by Olidimarra. As the trickster hid in the shadows, the goddess tormented the Magician. Just as she was about to destroy him, she reagined her composure and instead imprisoned him in the Cathedral's walls, condemning him to improve the temple during his every waking hour and threatening him under pain of eternal torment that he was never to leave the sanctuary he had built.
When Aerin'al departed, Olidamarra came forth demanded that the Magician uphold his end of the bargain. Bound by his sentence from Aerin'al, the Magician could not comply with the god and began to beg for mercy. Silently laughing, the Trickster told the Magician that he was moved by his pleas and would spare his existence but as rightful punishment that he would be forever cursed with the memories stolen from the Hauri. The Magician humbly agreed and Olidamarra departed.
The Magician has toiled under his madness ever since, using the innumerable memories of the Hauri to aid in the construction of the Cathedral's many additions. He never notices the visitors to the Cathedral. He just keeps working silently, slowly incorporating his insanity into the temple's design.
Today, the Lost Cathedral of Aerin'al Hauri is widely believed to be little more than a myth. Scholars tend to stumble across a reference or two to it in historical texts but few take them at face value. Among those who take the legends seriously, few manage to piece together more than a couple of facts about it. Even spellcasters cannot divine the truth to its existence; all but the most powerful divination spells fail to work when asked about Aerin'al.