Where is the exit?

Hint 1 of 5:

It's actually hidden in a secret passage.

Hint 2 of 5:

Hit the switch behind the desk.

Hint 3 of 5:

A wall will open temporarily.  Run in!

Hint 4 of 5:

Use the red card on the access switch.

Hint 5 of 5:

This will allow you to move the bookcase right next to the switch.