You know the pattern by now, right? Whenever you come across a locked door, send Joey in first.
As it happens, there's a note on the other side of the door that's a hint about the code for the door.
It says, "Remember Waterloo." Use Rosa's phone to Oogle "Waterloo" and discover that a famous battle there occurred in --
-- 1815. Click on the door to bring up the number pad and type it in. Rosa will enter the code for you automatically after this.
What is there to find in the dorm?