Adurdin's 1st Levelpack
In the beginning of the level, there is a sign that says "Mothership Control Room Authorized Persons Only". The worldmap was edited to change how some of the levels look, including ones that don't lead to a custom level when entered.
It's been uttered that this level requires considerable skill to complete and can be a bit plain in places.
Spoiler warning! This shows the whole level.