You should plan a day or more at MT St Helens.
The Olympic US 191 is not to be missed. Tatoosh Head is farthest west point in contigent US. Opposite of Florida. Several NPS campgrounds along loop.
Come to eastern Washington. Much of eastern WA is high desert. Visit Grand Coulee dam in the evening and after dark for laser show on face of dam.
US 2 over the Cascade Mtns Stevens Pass visit Leavenworth or travel over Cascades on WA SR 20 over North Cascades and visit Winthrop. Leavenworth has a Bavarian motif where Winthrop is a western motif.
Many of the state aprks are decent. Order the vacation guide from
Washington State