Travel to Nashville, St Louis, Kansas city, Omaha, Sioux falls. Then take I-90. Stop at the corn castle, and Mount Rushmore in South Dakota. Then Rapid city and head over to Yellow stone. continue north on I-90 stopping at Missoula, and then Coeur d'Alene is beautiful (if you have kids, spend a day at Silverwood).
And from Spokane to Seattle there are a few different things to see, mostly hiking depending on the time of year.
