Daring Do and the Catacombs of Causality

Hallway

You're standing in a large hallway. "Geography and Earth Science" is to the West, while "Physical Sciences" is East. Further down the hallway you can see a guard standing in front of a closed door.

Behind you is a glowing magenta portal, which presumably leads back to the real world. It covers the entire girth of the hallway, blocking what would otherwise be an exit leading out of the library.

Head North down the hallway.

Check out the Geography section.

Go look at the Physical Sciences books.

Walk South into the portal.