I've slept on the Harwich-Hook of Holland ferry a few times. It is very comfortable, and much quieter than a sleeper train -- it was like being in a slowly rock

I've slept on the Harwich-Hook of Holland ferry a few times. It is very comfortable, and much quieter than a sleeper train -- it was like being in a slowly rocking "cabin hotel", where you don't have a window and the room is tiny. (You can get a room with a window, but for an overnight trip it seemed a bit pointless.) I find it difficult to sleep on sleeper trains, and usually arrive tired at the destination. Where there is the option I will use a night train out of principle (it's still usually more comfortable than a plane) but, if I have time, a daytime rail journey is much nicer.