Libra Arcanum

The Libra Arcanum is the name of a book, but also the name of a pocket dimension which is contained within the book.
The Libra Arcanum is a pocket dimension created by the Havenite scribe Coridus Cairn. Coridus Cairn was a prolific scribe and expert linguist, who made it his mission to translate many books into Tyrranean. Cairn visited the Library of Mika'Zah, the Archives of Empyrean, the Starlight Monastery, and even the Esoteric Archives, in his ambition. He was aided by Secretkeepers, Shavhani librarians, Starlight monks, and rogue Denizens, who he enlisted on his way. All the books they translated were placed into the Libra Arcanum.
However, as the pocket dimension grew larger and larger to accommodate all the books, it became more unstable. Cravers of knowledge from across the realms wormed their way into the dimension, and infested it. Meanwhile in the real world, Cairn was pursued by all those who he had stolen knowledge from. Cairn and his allies retreated into the Libra Arcanum, never to be seen again. They were likely killed by extra-dimensional monsters. The Libra Arcanum, contained within his journal, was brought back to New Haven and secured in the Undervault.
The dimension has had a number of curators over the ages, but most don't last long. The Denizen Archivist Kal'Zaa is one of the few to hold the position and survive. He abandoned his position shortly before the book was recovered by Maximillian Sithwyr, who became the new curator.