Trouble 2 is an indoor level, it's the middle level in between Trouble 1, and Trouble 3, it either can be entered on the way to the Key, or on the way back to the Great Hall. It is the Second level on the Trouble Level Path, in Dark Castle. It has shown up in Dark Castle, and Color Dark Castle, and will show up in Return to Dark Castle.
Levels on the Path
Main article: Trouble Level Path