Is there any confirmation that the special effects will rely solely on high-tech window in the train? I think the simpler way to build this would be to have the train enter a tunnel. Then you could supplement the windows with robots, AA, 4D effects like "real rain", or "real frost" from a dementor attack using a chiller blast or something. So you have a train that looks and works mostly like a train, and a tunnel (or two tunnels, 1 for each direction) full of effects.