On leaving Seattle the Empire Builder to Chicago travels past the Pugent Sound and through the Cascades mountains on the first afternoon and evening. As their name suggests, there are cascades in the Skykomish river as it comes down the mountains towards the Pacific. The path the train tracks follow means that when selecting a seat, you have to decide between the Pugent and the river cascades, one is on the left the other on the right of the train. I had a seat on the left side when facing the direction of travel so got great views of the Sound.
As we entered the Cascades, my views were predominantly of the forest and mountains with some glimpses of the river, albeit calmer sections than those giving the National Park its name.