Hidden basement

The Hidden Basement is something that was initially talked about by one of the game's developers when he talked to an Xbox player during the Gaming With the Developers event. The dev rumored that there was a "hidden basement in New Haven" and was "inaccessible after a certain point". The majority of the details about the basement, including how to enter it, are still unknown, however there is an ongoing discussion on the Gearbox forums as to how to get into the basement.

The way to enter this basement is still unknown to the public, and its investigation is still ongoing.