Endless Athenaeum

The Endless Athenaeum is a secret realm in an undisclosed plane. It is an embodiment of the goddess Ioun, the Knowing Mistress.

Description
The Athenaeum is a dimly lit, Escher-esque, infinite library containing records of all that is known, tended and read by Ioun’s spectral, celestial servants. Stories of every life, from birth to death, exist as books written in various languages; near an entrance and near the center, the books are written in Celestial; a little farther out are some written in Abyssal. The bookshelves, which move on their own to rearrange themselves, are made of different materials: various woods, metals, and so on.

The realm is well hidden, as Ioun is still nursing a grievous wound dealt by Tharizdun during the Calamity and knows her enemies seek to finish her off. A Plane Shift to the Athenaeum takes noticeably longer than the spell usually does.

Draped with silk cloths from an unseen height, an 80-foot-deep bowl, about which cushions and tables manage to stand at various angles (with tea cups, writing implements, binding materials, etc.) without anything sliding "downward," serves as a common area, at least for the purposes of Vox Machina's visit with Ioun's avatar. If one heads toward the ceiling from there, there is a "mirror" of the library "upside down."

Background
Ioun was one of the gods who fought against the Chained Oblivion during the Calamity, around 800 years ago. She devised the Prime Trammels that could be used to help banish a god from the Material Plane. She baited the Oblivion to her central temple where Whitestone now stands. She was badly wounded by the rampaging god in that battle and has been recovering, in hiding, ever since.

Pelor told Vox Machina that Ioun had the design for the artifact necessary to banish Vecna, and gave them directions to a place near the Pools of Wittebak to find the key to her secret realm.

and
Pelor's directions led Vox Machina to Sprigg's home. Sprigg turned out to be the unwitting mortal "key" to Ioun's realm. Vox Machina and Sprigg entered the Athenaeum. Percy, who was able to read the life stories written in Celestial, found the existence of such complete records to be life-affirming: it meant no one is forgotten. Scanlan, with the assistance of his Ioun Stone, led the party directly to the common area where Ioun's avatar awaited.

Ioun found, of the people present, only the prolific storyteller Scanlan worthy of a trial to be her champion; Percy was too fond of keeping secrets. She challenged Scanlan to find the Tome of Isolation within her vast library and return it to her within one hour, or else find someone else ready to take the challenge. Scanlan found that continuously singing about the Tome he sought, especially with the aid of Mythcarver, attracted the spectral servants to assist him, and on the back of Vex's broom he raced to the appropriate bookshelf. Vex had to pick a virtually impossible lock to get into the case, then they raced back to the common area, just in time. Along the way, Scanlan learned that casting a sufficiently powerful spell into the Tome would reveal the book’s text.

For completing the trial, Ioun returned the Tome to Scanlan (it contained the Rites of Prime Banishment, needed to drive Vecna out of the Divine Gate) and granted him the Blessing of the Knowing Mistress. She imbued the mighty Grog with proficiency with blacksmithing tools, and incepted the design for Prime Trammels into the mad genius Percy, so that together they could forge the implements to make the Rites much more likely to succeed.

When Vax asked about Vecna, she told the story of the lich lord’s rise and fall in the Age of Arcanum, and noted that the Sword of Kas, though an evil weapon, could be a powerful tool to help take down Vecna, and it was lost in Thar Amphala.

Moments later, she sensed that Vecna had just completed the Ritual of Seeding to ascend to godhood, and urged Vox Machina to hurry and stop Vecna before he could fully come into his power through a "miracle of terror" that would attract mass worship. She painfully extracted from herself a fragment of divinity for use in creating another Prime Trammel, and gave it to Scanlan. Finally, she asked Sprigg to stay in her realm and help her tend to her books, and Vox Machina departed with a Plane Shift back through the Divine Gate to Sprigg's house.