I like the idea of building a cupboard with shelves. On the shelves are images, stacked up against the walls, heaped up on the shelves.
Perhaps have a fish eye lens (like the one in a front door) to allow someone to see into the cupboard. My grandad made a boat inside a box that could only be seen through one of these lenses, so I know it works. Artificial lighting would be needed – or perhaps a roof made of cellophane.
Black-and-white images, and colour images. Pictures of people lying on the shelves. Or tacked on with masking tape.
The carriages on the Tube are like a waiting room, for example, in a hospital. Or like one of those overful cemeteries I have seen, abroad...stacked up in a Portuguese cemetery, or heaped up like the gravestones in the Jewish cemetery in Prague.
Perhaps play with what can be seen in the cupboard...showing it through a semi-opaque mirror that only allows a partial view of the images inside. Or a painting of the cupboard, a big clinical picture, with images of people, and perhaps their imagined thoughts, added too...
Alternatively, have a cupboard that is empty inside, but covered with images of people on the outside, to show the emptiness at the centre of the journey...
