You (or someone in your group) must have completed The Boar's Head
Steps
Examine a Lockerbox in the southeast corner of the barracks ( 17, 0, 32 ) Copy/waypoint 17, 0, 32
Click on Rummage through the tattered clothing in the lockerbox: "After rummaging through the tattered clothes and avoiding critters you find a red marble"
Go to the boar's head you got the black marble from at ( -14, 0, 40 ) Copy/waypoint -14, 0, 40.
Examine the boar's head.
Click on 'Inspect the eyes'.
Place the red eye in the hollow socket.
The quest updates and completes.
You receive a library key, which grants you access to the library upstairs.
A swine fiend (31-32 ^^^) will spawn behind you. He does not see invis and you do not have to kill him.