[tevake]

The Seatle area is really beautiful, lots of good suggestions above.
The length of your stay and how much driving you want to do are factors.

Driving n/ s thru Seatle/ Tacoma can suck with traffic. So the ferries out thru the sound and into the straights is a good way to get around ans see the sights of the sound.
Tabs suggestions are good ones.

The most beautiful coastal area I experienced in the PNW is the northern part of Oregon. From Astoria down thru Tillamook truly exceptional. Would take some driving time to get over that way but very worth it.

Bob's tips did help me get to some cool areas in the northern Olympic peninsula , tap him for good local knowledge in that area.

You are going to have a lot of good choices.

Cheers Richard