"The Unknown Building" is a building found in Entry #68, and stands as a building utilized by Hoody as a home or resting place. The exact use or location of this building has not yet been revealed.
All that can be said about the building is that it has a bed, appears relatively empty, and seems to be located inside of a lot of brush. It is also apparent that Alex knows where the building is, as he casually strolled in to confront Hoody. Despite Alex knowing it's location, Hoody still appears to be using the building in Entry #73.
The entryway is clearly covered in dirt, and the back door has been broken off
The windows show aging and the glass has been broken, showing advanced age