I would visit Olympic National Park Elwa River section near Port Angeles, the Worlds largest science project is going on there. The USFS had construction companies tear out 2 Dams and two lakes and the Elwa River is running wild again for the first time in a hundred years. Very interesting all the changes the river has made at it’s mouth since the Dams were tore out! After leaving there take Hwy. 101 to Olympia via I-5 and take I-5 to MP 67 South on I-5 to White Pass and go over White Pass and your in the North Cascades avoiding Seattle, then Head North to Grand Coullee Dam!
