If, and that's a big IF, the weather is clear make sure you go up on the Space Needle. Amazing views as you can see from Canada down to Oregon and the Olympics. Speaking of, take the ferry across the Olympic peninsula.
If you like Asian food, go to Cheng's. Fantastic Mongolian style cooking with you picking out your own ingredients and spices.
Depending on the time of year you can go to the locks going into Lake Union and watch the salmon heading in on their way to the spawning grounds.
Ditto on Leavenworth, neat little town on the eastern side of Stevens Pass.
If you like to gamble, there's an Indian casino up near Marysville, about 30 miles north of Seattle.
And don't forget Pikes Place Market in downtown Seattle. You know, the place where they toss the salmon around? Lots of great shopping and fresh food there.
You could also run up to the town of Snohomish as they have kind of an antique shops area, plus a weekly car show I believe.
Its been a few years since I've been out that way, pretty close to 20 years now that I think about it. Used to live in Everett and worked in Seattle.