This picture is from a 2nd floor apartment in Colorado. 1st floor is empty, unoccupied retail space. In the apartment's kitchen area there is a enclosed area which is finished with what looks like mold resistant drywall:
In the box around this area, there is a small, green cap, which I have no idea about what it is for:
There is no discernible writing on it. I'd guess that it connects to the retail space below, but the space has never been used or rented.
Any idea what it could be?