This is the winch room.  The small yellow dot (digitally inserted, left center) marks the entrance to the room (the end of the drift leading from the entrance, past the obstruction).  The room probably measures at least thirty feet wide by about fifty feet from the photographer to the yellow dot.  The arched ceiling is about twenty feet at the apex.  The winze is under the ice in the front left of the picture, and the winch alcove is just out of the picture on the left.

The winch alcove.

Views of the winch.