I was in a windowless stateroom on a train car, with a definite, occasionally jostled sensation of forward motion. My clothes and other personal effects were more or less casually strewn around the room, as if I'd been there awhile. I was standing facing the direction of movement, when I suddenly became aware of a giant "hole" in the right wall of the train that I'd previously taken for a closet.
Looking through that hole I saw into another stateroom, on another train, parallel and immediately adjacent to the one I was on, and through that train into another one, and another one, and another, infinitely. I was essentially looking into an endless tunnel, the "walls" of which were the interiors of these successively pierced staterooms. All the trains were moving forward at the same rate, as if joined together, with no space between them. The trains were not "fused" together, however. If anything, they seemed "linked." There was an occasional jostling sensation that would ripple up and down the tunnel, as if one of the trains were occasionally hitting a bumpy section of track, etc.
I saw no people other than myself, and wasn't otherwise aware of any other people. The only sound was the sound of trains on tracks.
It occurred to me (in the dream) that if the trains stretched out infinitely in that direction, there was no room for a "world" out there--no grass or trees or mountains--just trains.
I never turned around, or looked over my shoulder, to see if trains stretched out similarly from the left side of my own train (or even to see if there was a hole there).
I stepped back from the hole and realized it was as high as the train itself, and very wide, and oddly shaped around its edge. The entire tunnel stretching off into the distance had this same irregular shape (i.e., every successive hole through every successive train wall had this same shape).
I saw a light at the end of the tunnel. I realized a train was coming toward me, through the tunnel, through the other trains, perpendicular to them. I realized that the outline edge of the holes (and thus the tunnel) was exactly "train shaped."
I figured I'd better clear away my clothes and other items from the path of the train that was about to pass through my stateroom. I began to gather things up here and there, but I wasn't fast enough. An old-fashioned black locomotive barreled into the room.
That was the end.
I keep wondering if there was a hole in the left side of my stateroom, for that train to continue through.