The Stygian Library

The Stygian Library is a creepily genteel dungeon set in an infinite extradimensional library. Each expodition generates its route as it explores, resulting in new locations being iscovered with every visit. Included within: 

• Systems for generating locations within the library, including Entrance Foyers, Map Galleries, Tea Rooms,  Planetariums, Calculation Engines, Phantom Databanks, Paper Beehives, Phantom Pumps, Jarred Brains and the Sheol Computer.
• 40 monsters tailored to the Library, including Lantern Bearers, Skeleton Crew, Origami Golems, Guardian Shades, Lost Souls, Ink Elementals, Animate Spells, Archivist-Liches, Infernal Merchants, Escaped Fictions, Educated Rodents, Conceptual Wells and the orders of Librarians themselves. 
• A system for searching for specific knowledge within the library's depths, as well as 30 unusual books and the secret knowledge they contain.
• Tables for generating treasure, dreams, rumors, and various other useful details.
• A unique class of Mummified Sages, post-human accademics who've dwelled in the Library for decades or more. 

It's a big spooky library full of dangerous knowledge, spiritual automata and ghost-fueled computers.

This got a Judge's Spotlight Ennie, which is nice.