I'm planning a Labyrinth that is a library that is so big it's caretakers live in it and it functions as a city.

I'm borrowing a bit from Terry Pratchett's L-space ideas. Books = Knowledge = Power = (Force x Distance / Time)  any large amount of written words gathered in one place will warp space and time.  I've got the entire economy relying on facts and information rather than coin (i think my players will starve).  Roving bands of creepy conservationists who preserve the books can show up to fight back dangers to them caused by mold or bugs or the PCs. Several trapped books to scatter about and at least one animated one. And a Mind Flayer doing some research in the library who's hands are a little tied since anything that harms another beings sentience is forbidden and faces harsh conciquences INSIDE the Library. 

Still trying to think of what the residents eat, going to have once ornamental now functional gardens scattered about, but which livestock would cause the least damage to books. 

I'm wondering if anyone has any other library flavored suggestions or ideas?

I found this library themed one-page dungeon the other day. It might make for a cool "lost section" of your library city. The boss at the end is a book with googly eyes that is also apparently a powerful lich-mimic. That should be fun to design....

Don't forget the Librarian! 

Also, if knowledge = power, then anything that wants power wants knowledge.  Likewise, if books = knowledge, then anything that wants knowledge wants books.  Furthermore, if the Library is the largest collection of books in the world, then anything that wants books wants the Library.  Therefore, if power = knowledge = books and the Library is the largest collection of books in the world, then anything that wants power wants the Library. 

Might do the libararian, maybe a call out at least. 

The Library is certianly very very rich in coinage, they obtain original books, copy and distribute those copies. Which is profitable but who knows how accurately they copy, what they redact. How many books they keep off the public shelves.  

Anyone who wants the library is going to have a very difficult time taking it from the current owners. Players are a bit low level to be messing with anything that macro but might bring it up later. 

The point is that anything that wants power is going to be interested in the Library, including L/G wandering heroes who want more power so they can take out more-powerful bad guys. 

First off, I think the premise you've put forward is really cool. I love the idea! As for livestock, depending on the size of the gardens, cows would be a source of milk, beef, and leather from their hides, using the chemicals from the veggies and fruits to tan the leather. 

I'm imagining them needing to be extremely self-sufficient, so maybe they are vegetarians - because taking care of animals would take up precious time and resources that could be spent collecting more knowledge. Perhaps they grow the staples, and also some specific fruits, veggies, and plants that can be made into paper, leather, glue, thread, or pressed into some type of hard board for binding.

Hope that's helpful!

Minor cool stuff you could include:

• At some point, there has to be a secret door activated by pulling out a particular book from a bookcase. Players would probably identify which one by solving a puzzle or riddle.
• Book based traps? E.g. what looks like a powerful spell book is actually a magical trap which casts banishment on the one who opens it
• If words are powerful maybe famous last words, i.e. people who died in the library, continue to haunt it as spirits? Constantly re-enacting their last moments, attacking anyone they come across. You could even have a trapped soul whose last words were an unfinished sentence - the party needs to complete it for them by uttering the right words to put their spirit to rest

Quote from Mittens >>

As for livestock, depending on the size of the gardens, cows would be a source of milk, beef, and leather from their hides, using the chemicals from the veggies and fruits to tan the leather.

I am commenting so I can find this discuss again later. Love yhe ideas included and I'm going to have to design something similar now. 

Also a note to help with the food idea, every library's gardening section includes books on composting and green living, and in a fantasy world getting this information from druids or nature guardians carry traces of natural magic. Maybe these concepts are potent enough that they bring themselves to life and the party can find whole sections of the library where open books show vast gardens and forrests that the librarians can step into and bring out items they need for sustenance and materials for printing and preserving books. There is also no way to have a library of this magnitude in a world with a panteon of gods and at least one of them not have a hand in this in some fashion, maybe they are the ones who enforce the rules of knowledge and not hurting intellectuals. 

Your labyrinthine library city sounds like a captivating blend of knowledge and adventure, with a touch of Pratchett's L-space brilliance! The way you've woven books into the very fabric of your world is truly remarkable. Perhaps you could introduce a guild of leatherworkers, utilizing the library's vast collection to source materials for creating intricate book covers and parchments. This way, you're not only preserving knowledge but also turning leather into an art form that binds your city's past and future. As for sustenance, consider cultivating silk-producing creatures like silkworms in your gardens – a delicate balance between nature and the written word. It's inspiring to see how you're crafting a universe where leather, lore, and life intersect in such imaginative ways.

For mechanics 

• Travelling through books. This can take the form of a fairy tale world like candlekeep mysteries or a labyrinth made of scribbles and text. They can essentially act like a portal connecting two places. 
• Fictional characters brought to life. You can have illusions or book constructs take the form of book characters and interact with the players whether in combat or otherwise. A swirl of errant papers combine in the form of a dragon or a night for example. 
• A powerful librarian guardian who applies rules like being quite or not damaging books. A pretty classic example would be a dragon that applies these rules like a ghost dragon

For monsters

• Pft2e  has  a fun monster that is basically book eating gremlins called scrit. In dnd you could flavor a boggle to be mechanically similar.
• A junk golem made of  old books and abandoned spell scrolls. Take something like the flesh golem take away the immunity to lightning as that doesn't make sense for books and describe it as a living pile of books. There is also  the Grisgol which is a much more powerful version
• Giant book worms or giant constrictor snake that looks like a worm.
• living spells that escape from spell books like living burning hands
• dust mephit hiding in the dusty neglected spots.  
• nothic or mad wizards

As for traps 

• collapsing piles of books. Possibly a big mountain players need to climb over that will collapse on them 
• cursed books that draw in readers similar to antipathy/sympathy possibly leaving them trapped for ever reading it or applying some other effect liked madness
• dusty sections where a commotion makes an obscuring cloud of dust. The dust  could cause choking  with the mechanics of [magicitem]dust of sneezing and choking[/monster], it could prevent invisibility by coating players or block sight. 
• Books that are actually monsters like mimic or animated books