I had a question about those carriages that are described as having a corridor down the left side. In all these carriages, does the wall on the left side of the corridor have windows to the void? Or is it just a blank steel wall?

The ones I was looking at were Coaches A, C, D, J, K, and M. That is, the Quiet Coaches, the Sports Gym, possibly the Medical Coach, the Music Coach, the Libraries, and the Spa. Not all of these would be good choices, but if in any of them, there were no windows to the Void, that outer wall in the corridor would be a possibility for the mural.

I don't think Rapunzel and Curufin would want to hang the mural over windows.