The library is located in the Desert Dungeon, underneath the Jakundaf Desert. The door is locked and you need silver key 4009 to open it.
First of all, talk to Hagor in order to get key 4022. Once you have it, you can access the locked room where key 4009 is.
The library door is four floors below groundlevel. First you have to did your way into the desert dungeon by the ruins. Go down all holes until you are 5 levels down. Go north and follow the wall that is to your left (will be on your right when you've followed it around and start to go south). It will lead you past a beholder spawn and eventually to a ladder. Go up here and follow the tunnel. Go north when the path split and you will come to the door. This is where you need to use key 4009.
Desert Dungeon Library
These bookcases are EMPTY:
Nineth, Twentith, Twenty-Eighth, Thirtieth, Thirty-Fifth, Fourtieth
Library Content
First bookcase
Dangers of Adventures 1 (book)
Second bookcase
Book Review of Netlios Opus (book) Template:Infobox Book/List
Third bookcase
Template:Infobox Book/List
Fourth bookcase
The Adventurer's Guide to the Dungeons (book)
Fifth bookcase
Potion of Invisibility (book)
Sixth bookcase
On Mixing Potions (book) Important Facts from Galactic History 2 (book)
Seventh bookcase
Potion of Happiness (book) Potion of Flight (book)
Eighth bookcase
Dangers of Adventures 4 (book)
Tenth bookcase
On Different Fluids, 2nd Publication, Part One (book)
Eleventh bookcase
Dangers of Adventures 2 (book)
Twelfth bookcase
Potion of Silence (book) Template:Infobox Book/List
Thirteenth bookcase
Template:Infobox Book/List
Fourteenth bookcase
Adventurers Guid Through Tibia 1 (book) Dangers of Adventures 3 (book)
Fifteenth bookcase
Potion of Fast Movement (book)
Sixteenth bookcase
About the True Nature of Objects (book)
Seventeenth bookcase
Template:Infobox Book/List
Eighteenth bookcase
Dangers of Adventures 2 (book)
Nineteenth bookcase
On Different Fluids, 4th Publication (book)
Twenty-First bookcase
Template:Infobox Book/List Template:Infobox Book/List
Twenty-Second bookcase
Potion of Hallucination (book)
Twenty-Third bookcase
On Different Fluids, 1st Publication (book)
Twenty-Fourth bookcase
Potion of Regained Vision (book)
Twenty-Fifth bookcase
Important Facts from Galactic History 1 (book)
Twenty-Sixth bookcase
On the Game Tibiaball (book)
Twenty-Seventh bookcase
On Different Fluids, 3rd Publication (book)
Twenty-Nineth bookcase
Template:Infobox Book/List
Thirtieth bookcase
Potion of Demonic Transformation (book)
Thirty-First bookcase
Template:Infobox Book/List
Thirty-Second bookcase
Thirty-Third bookcase
Adventurer's Guide to the Dungeons (book)
Thirty-Fourth bookcase
On Different Fluids, 2nd Publication, Part Two (book)
Thirty-Sixth bookcase
On Different Fluids, 5th Publication (book)
Thirty-Seventh bookcase
Potion of Recall (book)
Thirty-Eighth bookcase
Potion of Future-Vision (book)
Thirty-Nineth bookcase
Template:Infobox Book/List
Fourty-First bookcase
About Strange Mechanisms (book)
Fourty-Second bookcase
Potion of Living Dead (book)