Okies, first thing that hit me was the writing on the door. It's the only text in the entire thing and it warns not to open the door... Now, since the door is open, the first thing I feel from this is the rebellion, betrayal, escape, anything and everything that goes with opening something that shouldn't be opened or releasing something that shouldn't be released. From the door, vectors carry the eye towards where the door is opened. I think it's very well captured that the door opens towards the big drum and what looks like the light from the street. So the escaped (whatever) has gone and is out of where they were held?
There are probably about 40,000,000 interpretations of this piece, but I think that the use of natural light, black and white, focus and strange, almost moving angles make this picture surprising, in that in what the picture shows directly, which is disgusting filth, is a story or a snippet of freedom and escape.