I’ve spoken to a lot of Amtrak employees and they all tell me that the California Zephyr route from Chicago, IL, to Emeryville, CA, is the absolute prettiest route. It goes through scenic mountains and tunnels. The second most beautiful route is the Empire Builder which goes from Chicago, IL, to Portland, OR, or Seattle, WA. This train goes through Montana etc. and it’s supposed to be amazing. This route also runs near Glacier National Park, if you want to stop there.