The Space Needle might be a cliché, but it is an absolutely gorgeous view of Seattle and Puget Sound if you can make it up to the top of it. The area around it has a series of neat museums and art displays, as well, to round out a half-day visit to it.
If you are into wine and/or pretty rural scenery, I would recommend going a little to the west and south of Portland on the way to Salem through this area...
View attachment 64812
...on the bank of the Willamette Valley. Oregon has something of a "Napa North" in that region, founded by some California expats who headed north, and it is some of the most beautiful scenery you are going to find on this continent, too, while you are there.
Here is a more specified map/site...
https://www.winesnw.com/mid-will_vly_eola_amity_district_mcminn_map.html