Project X - The Mystery of this Windowless New York Skyscraper

There is a mystery building in lower Manhattan that has caused much conversation and speculation over the years. The windowless skyscraper that has been referred to as the the "long lines building", Project X and Titanpointe.

What actually goes on inside? Who owns the building? Why doesn't it have any windows? The building is so unusual that it's presence prompted Tom Hanks to Tweet about it a few years ago.